I respect your opinion, please do not speculate on what Guru Ji couldn't have done. Basing on Bachittar Natak, please do not negate the purpose of Khalsa. Same Guru also says" Manas kee jaat sabh ek hee pehchanove(close to it). In a society deeply drowned in castye system, how a low class family could have dared to offer a daughter for the Guru bridegroom when so called Kashattryas were doing all the spoon feeding to marry off their daughters in Guru ghar? Ponder over it before concluding your judgment on Guru's marriages. Guru Sahiban were a way above this filth.
Well my opinion is based on the society the Guru jis lived in and also the traditions tha they followed and were brought up in.
And for khalsa, I have not negated it at all, I have just supported the warrior influence and tradition of khalsa, Guru ji has also acknowledged his warrior heritage:
Sri Dasam Granth Sahib
ਸਵੈਯਾ ॥
सवैया ॥
SWAYYA
ਛਤ੍ਰੀ ਕੋ ਪੂਤ ਹੌ ਬਾਮਨ ਕੋ ਨਹਿ ਕੈ ਤਪੁ ਆਵਤ ਹੈ ਜੁ ਕਰੋ ॥ ਅਰੁ ਅਉਰ ਜੰਜਾਰ ਜਿਤੋ ਗ੍ਰਹਿ ਕੋ ਤੁਹਿ ਤਿਆਗ ਕਹਾ ਚਿਤ ਤਾ ਮੈ ਧਰੋ ॥
छत्री को पूत हौ बामन को नहि कै तपु आवत है जु करो ॥ अरु अउर जंजार जितो ग्रहि को तुहि तिआग कहा चित ता मै धरो ॥
I am the son of a Kshatriya and not of a Brahmin who may instruct for performing severe austerities; how can I absorb myself in the embarrassments of the world by leaving you;
ਅਬ ਰੀਝ ਕੈ ਦੇਹੁ ਵਹੈ ਹਮ ਕਉ ਜੋਊ ਹਉ ਬਿਨਤੀ ਕਰ ਜੋਰ ਕਰੋ ॥ ਜਬ ਆਉ ਕੀ ਅਉਧ ਨਿਦਾਨ ਬਨੈ ਅਤਿਹੀ ਰਨ ਮੈ ਤਬ ਜੂਝ ਮਰੋ ॥੨੪੮੯॥
अब रीझ कै देहु वहै हम कउ जोऊ हउ बिनती कर जोर करो ॥ जब आउ की अउध निदान बनै अतिही रन मै तब जूझ मरो ॥२४८९॥
Whatever request I am making with my folded hands, O Lord ! kindly be graceful and bestow this boon on me that when ever my end comes, then I may die fighting in the battlefield.2489.
Again for the quote of humankind, I have seen that so many people have taken it out of context and only taking the ਮਾਨਸ ਕੀ ਜਾਤਿ ਸਬੈ ਏਕੈ ਪਹਿਚਾਨਬੋ Manas kee jaat sabhey ekai pehchanbo partof the line, just to justify it for caste system only, instead of the whole line:
ਹਿੰਦੂ ਤੁਰਕ ਕੋਊ ਰਾਫਜੀ ਇਮਾਮ ਸਾਫੀ ਮਾਨਸ ਕੀ ਜਾਤਿ ਸਬੈ ਏਕੈ ਪਹਿਚਾਨਬੋ ॥
हिंदू तुरक कोऊ राफजी इमाम साफी मानस की जाति सबै एकै पहिचानबो ॥
Someone is Hindu and someone a Muslim, then someone is Shia, and someone a Sunni, but all the human beings, as a species, are recognized as one and the same.
And in this context, Guru ji has actually used ਮਾਨਸ ਕੀ ਜਾਤਿ ਸਬੈ ਏਕੈ ਪਹਿਚਾਨਬੋ Manas kee jaat sabhey ekai pehchanbo in a much different context than just caste system.
And of course we can get an even better picture with the whole pauri (and i also posted the next pauri because i also like the message it teaches) :
Sri Dasam Granth Sahib
ਕੋਊ ਭਇਓ ਮੁੰਡੀਆ ਸੰਨਿਆਸੀ ਕੋਊ ਜੋਗੀ ਭਇਓ ਕੋਊ ਬ੍ਰਹਮਚਾਰੀ ਕੋਊ ਜਤੀ ਅਨੁਮਾਨਬੋ ॥
कोऊ भइओ मुंडीआ संनिआसी कोऊ जोगी भइओ कोऊ ब्रहमचारी कोऊ जती अनुमानबो ॥
Somebody became a Bairagi (recluse), somebody a Sannyasi (mendicant). Somebody a Yogi, somebody a Brahmchari (student observing celibacy) and someone is considered a celibate.
ਹਿੰਦੂ ਤੁਰਕ ਕੋਊ ਰਾਫਜੀ ਇਮਾਮ ਸਾਫੀ ਮਾਨਸ ਕੀ ਜਾਤਿ ਸਬੈ ਏਕੈ ਪਹਿਚਾਨਬੋ ॥
हिंदू तुरक कोऊ राफजी इमाम साफी मानस की जाति सबै एकै पहिचानबो ॥
Someone is Hindu and someone a Muslim, then someone is Shia, and someone a Sunni, but all the human beings, as a species, are recognized as one and the same.
ਕਰਤਾ ਕਰੀਮ ਸੋਈ ਰਾਜਕ ਰਹੀਮ ਓਈ ਦੂਸਰੋ ਨ ਭੇਦ ਕੋਈ ਭੂਲਿ ਭ੍ਰਮ ਮਾਨਬੋ ॥
करता करीम सोई राजक रहीम ओई दूसरो न भेद कोई भूलि भ्रम मानबो ॥
Karta (The Creator) and Karim (Merciful) is the same Lord, Razak (The Sustainer) and Rahim (Compassionate) is the same Lord, there is no other second, therefore consider this verbal distinguishing feature of Hindusim and Islam as an error and an illusion.
ਏਕ ਹੀ ਕੀ ਸੇਵ ਸਭ ਹੀ ਕੋ ਗੁਰਦੇਵ ਏਕ ਏਕ ਹੀ ਸਰੂਪ ਸਬੈ ਏਕੈ ਜੋਤ ਜਾਨਬੋ ॥੧੫॥੮੫॥
एक ही की सेव सभ ही को गुरदेव एक एक ही सरूप सबै एकै जोत जानबो ॥१५॥८५॥
Thus worship the ONE LORD, who is the common enlightener of all; all have been created in His Image and amongst all comprehend the same ONE LIGHT. 15.85.
ਦੇਹਰਾ ਮਸੀਤ ਸੋਈ ਪੂਜਾ ਔ ਨਿਵਾਜ ਓਈ ਮਾਨਸ ਸਬੈ ਏਕ ਪੈ ਅਨੇਕ ਕੋ ਭ੍ਰਮਾਉ ਹੈ ॥
देहरा मसीत सोई पूजा औ निवाज ओई मानस सबै एक पै अनेक को भ्रमाउ है ॥
The temple and the mosque are the same, there is no difference between a Hindu worship and Muslim prayer; all the human beings are the same, but the illusion is of various types.
ਦੇਵਤਾ ਅਦੇਵ ਜੱਛ ਗੰਧ੍ਰਬ ਤੁਰਕ ਹਿੰਦੂ ਨਿਆਰੇ ਨਿਆਰੇ ਦੇਸਨ ਕੇ ਭੇਸ ਕੋ ਪ੍ਰਭਾਉ ਹੈ ॥
देवता अदेव ज्छ गंध्रब तुरक हिंदू निआरे निआरे देसन के भेस को प्रभाउ है ॥
The gods, demons, Yakshas, Gandharvas, Turks and Hindus… all these are due to the differences of the various garbs of different countries.
ਏਕੈ ਨੈਨ ਏਕੈ ਕਾਨ ਏਕੈ ਦੇਹ ਏਕੈ ਬਾਨ ਖਾਕ ਬਾਦ ਆਤਿਸ ਔ ਆਬ ਕੋ ਰਲਾਉ ਹੈ ॥
एकै नैन एकै कान एकै देह एकै बान खाक बाद आतिस औ आब को रलाउ है ॥
The eyes are the same, the ears the same, the bodies are the same and the habits are the same, all the creation is the amalgam of earth, air, fire and water.
ਅਲਹ ਅਭੇਖ ਸੋਈ ਪੁਰਾਨ ਅਉ ਕੁਰਾਨ ਓਈ ਏਕ ਹੀ ਸਰੂਪ ਸਭੈ ਏਕ ਹੀ ਬਨਾਉ ਹੈ ॥੧੬॥੮੬॥
अलह अभेख सोई पुरान अउ कुरान ओई एक ही सरूप सभै एक ही बनाउ है ॥१६॥८६॥
Allah of Muslims and Abhekh (Guiseless) of Hindus are the same, the Puranas of Hindus and the holy Quran of the Muslims depict the same reality; all have been created in the image of the same Lord and have the same formation. 16.86.
Also, for Guru jis to follow their tradition, it would not have neccesarily meant following caste system, and instead just respecting their linage and traditions, so of course they were above the filth of looking at people as higher or lower, but respect is different, and we should all respect the desicions and laws of parents and government. Gurus had to respect their families wishes and could not reject their duty. Guru Nanak had to get married as it was his parents wished, and guru ji showed respect towards his parents. Guru Gobind Singh had to create Khalsa, to protect the socity and to protect dharam. Guru jis followed dharam. It was also their dharam to marry in their tradition, it would have been adharam for them to disobey their parents and family desicions. It is also adharam for us to disobey our own parents. Remember, many people follow adharam in this day and age, even the people that are called as religious, since it is the Kaliyuga/Kalijuga. Guru jis were binded to their human bodies as long as they were in human form (when and if they were able to leave their bodies, then circumstances change of course). Also as citizens we have to follow the law of our countries.
Also, to into caste system. You and I know, that it is evident in gurbani, that Guru ji has respected the 4 varnas equally. They have spiritual equity.
Adi Guru Granth Sahib p747
ਖਤ੍ਰੀ ਬ੍ਰਾਹਮਣ ਸੂਦ ਵੈਸ ਉਪਦੇਸੁ ਚਹੁ ਵਰਨਾ ਕਉ ਸਾਝਾ ॥
खत्री ब्राहमण सूद वैस उपदेसु चहु वरना कउ साझा ॥
Kẖaṯrī barāhmaṇ sūḏ vais upḏes cẖahu varnā ka▫o sājẖā.
The four castes - the Kh'shaatriyas, Brahmins, Soodras and Vaishyas - are equal in respect to the teachings.
ਗੁਰਮੁਖਿ ਨਾਮੁ ਜਪੈ ਉਧਰੈ ਸੋ ਕਲਿ ਮਹਿ ਘਟਿ ਘਟਿ ਨਾਨਕ ਮਾਝਾ ॥੪॥੩॥੫੦॥
गुरमुखि नामु जपै उधरै सो कलि महि घटि घटि नानक माझा ॥४॥३॥५०॥
Gurmukẖ nām japai uḏẖrai so kal mėh gẖat gẖat Nānak mājẖā. ||4||3||50||
One who, as Gurmukh, chants the Naam, the Name of the Lord, is saved. In this Dark Age of Kali Yuga, O Nanak, God is permeating the hearts of each and every being. ||4||3||50||
Also research and traditions show that these 4 varnas weren't really a system of hierarchy, and more of a way of generalising people of the 4 ways of their duties, where Brahmins would be people who were learned/gyanis, and kshatriya being the warriors, sometimes with people even being able to jump to a different varna.
Bhai Gurdass has also gone into details of the different castes/tribes/jobs of the 4 varnas, in his vaaran.