I believe this 'ghetto mentality' to which you refer, will only influence you if you decide to remain within the confines of your current social circle [which i assume is all your wonderful friends joining you at UCL :-p] .
I also think you don't respect UCL as a university because of the amount of people you know who were offered places (people whom you consider not academically capable). Whereas you noticed alot of people rejected from 2nd rate US universities. I'd like to venture a theory that it was more due to your academic background - CIS doesn't translate its transcripts well towards American universities as it is more geared towards sending students to the UK. As a result, a lot of capable candidates were rejected from US universities they clearly deserved to be in. UK focuses solely on academics for international students ; so all students getting 8A's at GCE , 4 A's at A/S are differentiated based on their personal statement. which clearly isn't fair.. but thats how life goes.
I'd say UCL's a better university(in a completely different league).. but for your personality and certain personal reasons.. go to USC if you think its better for you.