alright aad002 ji, I will try and talk about some of the matters that you have discussed, and there is no offense taken at all;
One thing to remember is that there are many more hindus and muslims than there are sikhs, so it would be more difficult to generalise them having the same view based on just some of them, as opposed to sikhs.
Secondly, there are also other questions to ask from my observations and from what I have been taught, like how traditional the families are, and then from that you could also find out how conservative and liberal they are, this is also influenced by background, including tribe/race/caste, where they come from (pind/city/country), and also how many generations they have lived out of india or even out of pind, and even if thery came from poverty/ghettos or from a stable background and good area.
Then you will see that the more traditional families will tend to marry in same
tribe/race/caste/nation/country/group, but even other people tend to at mostly marry in the same nation, or skin colour, or something else, like same panth, usually if it counts as a "major religion", or more usually to panthic/religious tribalism.
Since a marital ceremony is a tradition for many traditional peoples of the world to start a partnership, then not only do non/less-traditional people not really need to marry within the same group, they don;t really need to get married at all. As you see, in many places such as western countries, to have a partnership, marriage is not seen as important, as people do a thing called dating instead, where they can just easily be partners by being boyfriend and girlfriend, which starts without ceremony and without the need for family involvement like marriage has to start it.
Also you will see in the areas such as the pinds/villaged there are many differences in cultural values and traditions, and even the way language is spoken, between the different tribes present in the pinds.
And as well, Guru jis into married to kshatriya and by kshatriya tradition, as this was the cultural thing to do, and since Guru jis lived and were brought up in kshatriya families and values. Even the making of Khalsa fauj was very influenced by Guru Gobind Singh ji's Kshatriya/warrior heritage and was a revitalisation of this warrior kshatriya heritage of the indian society. And this is evident when Guru ji talks about his royal Suryavanshi kshatriya lineage in Bachittar Natak, I also believe there is mention of something in Bhai Gurdas ji diya vaaran.
Also, most people who go for the out of caste marriages are also the ones who fit into the more liberal category, such as ones doing the things like dating, as it is rare to to find inter-caste arranged marriage. The sikhi being taught is very khalsa warrior oriented these days, and so this helps sikhs in some aspects being dharmic and annakhi, and this would somehow influence more towards conservative attitudes, resulting in preference for arranged marriage and being against behaviour seen as liberal such as dating, women drinking and wearing obviously revealing clothes such as skirts and showing off a bit too much in other parts of the body. Tradititional indian families such as mine and some of my relatives and many others, see many religious or even amrit-dhari families and amrit-dhari singhs/singhnis behaving in these liberal ways, and see it as shocking, since to us it is taboo, but yet much more religious families are out of tocuh with their culture. In this case it can also be seen, that people have forgotten how to be dharmik, and instead try to be religious, since in west there is more religion than dharam. And it is very much possible, and I see it all the time, in the so-called "religious" people behaving in adharmik ways.
And as you said, romantic attraction has become a major point in finding a partner, and unfortunately it has taken too much improtance. That is another reason helping people marry out of caste/tribe/race. But this romacne thing is making people rush into things, and people aren't prepared to make the effort to make a partner, and instead just go for whatever pretty face that they have some chemistry with. For me personally, there is no real rush/reason to need to marry out of caste/tribe/race, but it might be different froms some people. For peopel who have become too liberal and out of touch witht heir tribal values, culture and traditions, then I would say that they might as well go ahead and marry whoever. But remember, this is more of a case of assimilation, and I personally believe in integration over assimilation. From our Gurus I have learnt to be against assimilation, such as islamic assimilation by the mughals, or assimilation by the British in their raaj.
But regardless, I am pretty much sure that guru jis would never have married out of kshatriya and I wouldn't see the need for them to either.
Religious/panthic tribalism
There is an unfortunate side to this, as the tribalism has increased from being limited to caste/tribe to encompassing a whole panth. Of course, describing a panth in the western context of faith/religion only adds to this tribalism; but that is not a discussion for this thread.
So you will see this tribalism seen even in the sikh rehat maryada created by the SGPC, where its mentioned that sikh can only marry sikh. So, you see, now people have started treating their panth as a caste, treating being sikh as a caste. This is how things have become, whereas before British influence in sikhi, there would have been absoultely no problem in sikhs and hindu marriage. So you see this "problem" has gone from being at a caste/race level to a panthic level.
Cases of marriages out of caste/tribes
So, there is cases where people even in India and pinds/villages have to marry out of caste. Such as punjabis bringing (or buying?) a woman from Bihar or Gujarat to marry. Also, there was a case I was reading, where Rajputs started marrying jatts, since many other rajputs had become muslims. I mean, there have been circumstances where it is acceptable. Maybe even this shortage of girls now in punjab could be a valid circumstance. I would happily believe that there was probably marriages between different tribes, or tribes and groups being created out of other groups.
And remember, it is tradition again, for the woman to become part of the tribe she marries into. This is evident, in the woman taking the clan name of her husband, which is easily seen even in the western countries.
Finally, some tribes do have enough similar cultural values and traditions for them to marry with each other, so you will see that in some castes/tribes/races marriage to another group is more acceptable and regular than others.
