Wow - there's a lot of ignorance about hip hop.
Basically, first thing, there will always be genres of music that you understand, and genres that you don't. You should give each genre a try, and if you still don't get it, you should recognise that it's just not for you. For the same reason, I will never criticise metal or country music even though I totally don't get the point.
Second, there are the different elements of music: melody, rhythm, harmony, texture. Obviously rap has little to do with melody, so criticising rap music on that count is as daft as criticising classical music for not making you shake your ass.
Rap music is not always simple, as anybody who has listened to "Fear of a Black Planet" can tell you. At any one point there would be five or six things going on at the same time you need a very good ear to keep track.
Hip hop is usually derived from many other things: mainly jazz, funk, soul. If you like these genres, you should definitely give hip hop a try. But hip hop by its nature will encompass everything, because hip hop is about everything. Hip hop has been fused with classical music before ("Unfinished Sympathy"), heavy metal ("Bring tha Noize", Anthrax version), 80s pop music ("street dreams"), broadway musicals ("Hard Knock Life"). The range of possibilities for hip hop makes it a very creatively fertile genre.
Hip hop isn't all about guns and pimps and hos, although the extent to which these themes dominate hip hop is not a good trend. There is a lot of political commentary (not that Singapore music knows anything about that), some humorous and philosophical stuff. Hip Hop is not about being emo, but then again Metal is not about being happy - many genres of music cover less than the full range of human emotions. If you listen to A Tribe Called Quest, De La Soul, Madvillian, it's not always gangsta rap.
I went to the George Clinton concert in 2008. It's a good thing that there were so few hip hop fans in Singapore that when a hip hop legend comes to Singapore, nobody turns up and I get my cheap seats upgraded. I saw a youtube clip of Najib Ali attempting to get George Clinton to rap to "Why u so like dat?" Now that is daft for several reasons. First, George Clinton doesn't rap. He makes a lot of great funk music which is sampled by hip hop artists. You know that when you're ranking universities, you count the number of times a scientific paper has been cited? Well in hip hop it also works like that. George Clinton is a legend in hip hop because parliament funkadelic has been sampled more than anybody else other than maybe James Brown. Second, that is plain disrespectful. I like "Why U So Like Dat" as a novelty record but it is really crap compared to what George Clinton has done in the past. It's as though Mozart were visiting Singapore and you're asking him if he can sing "I'm Too Sexy". But I also felt sorry for the Kopi Kat Klan.
But on the whole I felt that the whole episode reflected badly on Singaporeans' ability to understand hip hop.