I think what most people do is compare the two, those who do this are wrong. Music is music. No genre is better than the next, they both convey messages. One irks me, some beats my take 4 seconds, but Rap isn't all about the beat, it's about the lyrics, not all raps are about getting money and weed, listen to Shing02, listen to Big Daddy Kane, the time in which the music is made, doesnt remove it from the genre you can't say, oh i like classic rap like 90's. Rock has some trashy shit as well, don't just bash hip/and rap and turn a blind eye to green day and my chemical romance and stuff like that. Certain things in rap and hip hop may suck, thay suck, but your saying a whole music form sucks, your saying what the west side(coast) connection and tupac and big daddy kane and people like that worked hard to promote, not because they thought rock sucked, but because they had a love for the art form, i dont go around saying that techno sucks or video game music is trash(i like them both so dont trip) just because i like rap more, your acting pretty in mature for the fact that your are not respecting the art form, as bad a s lil wayne sucks, he is even into rock because it is a form of music(or because he wants to destroy that to). You obviously have a lack of knowledge when it comes to rap, and music.
Rap is Rhythm and Poetry(literal). And if im not mistaken, rock is the same thing. Now some people are just to narrow minded, when they think of rap, they either think of lil wayne, or some gangster with his jeans sagging and a forty in one hand and a gat in the other(meh bro just said that). Have a nice day people.

********UPDATE*********
Note that those who truly hate rap/hip hop are in a part of a very small percentage. It's different to not like it in the state it's in now, but to judge it entirely just off of mainstream rap, and that only, is just plain stupid. You don't have to like it, there is some country I don't like, but I actually listen to it more now than I did when I was younger. The two genres have a lot in common(in terms of mainstream lyrics). The only sad thing I can think about rap and hip hop now is that there are some people with really great potential but are shunned because either their style is TOO original, or what they are saying doesn't appeal to the mainstream audience. It sucks, but the mainstream audience has the greatest voice, as long as they like what isn't really respected by other cultures, then they are just gonna dig ourselves into a hole. Like I said, I listen to all music, and for those who say rap isn't music, you are fools. Rhythm is all that is needed for something to be a song. I don't think I have to go any further into that. Last bit before I go, I just wanna see people with more of an open mind, not to just music, but everything. I don't like seeing someone while I'm with my friends and theyire like oh you know he listens to" ", or does" ". I think everyone would be much happier if we learned to accept everything. Just because you accept it, doesn't mean, like I said, doesn't mean you have to be like 100% THIS IS THE GREATEST THING EVER.