I am a member of the freethought society, which could be considered to be a part of the religious community. it is a society of "freethinkers" who are essentially athiests, but not necessarily. we have events such as debates, panels and move screenings on campus. i'm not involved with any other groups of that kind on campus, but I know that LGBT is very active here.
I think perhaps very conservative/right - wing students might not find as large of a contingent here at say a school in the south. but that doesn't mean that it doesn't exist, it's just a much quieter group. I think anyone looking for a big school with an amazing football team that everyone cares about would be unhappy here, but athletes are not hard to find here.
There is of course self segregation and bonding among pupils of similar ethnic or racial backgrounds, especially since there are clubs for just about every brand of asian, east asian, south asian, latino and african american on campus, but its not unusual to see interracial couples or groups of friends who are of mixed races. it's not really something that is thought about here - your friends are your friends, color isn't typically a factor.
Four tables question - One table would be a group of jewish girls. most of whom are probably wearing uggs, but not exclusively. north face will also probably be well represented at this table, as will scarves and some kind of shoulder bag. the next table might be a table of football players. (or any athletic teams - they tend to have team meals in the dining halls) teams don't tend to be too raudy, but are easy to spot in the crowd because of size, attire or shaved heads (swimmers). the next table may be a mix of people who you couldn't identify, there will be different races, religions and styles of dress, most of which are probably nondescript. and i guess a table with one or two people listening to music and doing homework.
i would guess that an upper middle class background is most prevalent, but not the only one. it's not typically discussed, so i honestly couldn't say what background most come from unless i were to make an assumption about the town they were from or the clothes they wear (which isnt something tufts students tend to do) no one talks about how much money they will make in the future. students are incredibly aware of politics and many are very active in the tufts democrats, republican or even socialist groups. there are mock debates on campus and any kind of political event going on in boston will result in a group from tufts attending.