I get to level 55 in 5 levs and im going to make a Death Knight for tanking and PvP, so i wanted to know why they get so much abuse?

Most definetly because they were overpowered. Since you start off with better armour and weapons than everyone else, they are envious

because people dont know how to play them properly. And DK tanks are a pain in the butt half the time. Be ready to get some hate. And just roll with it because its never going to stop. Around level 58 to like 65 its going to get annoying because youre going to have mostly DK's in your party and you got noob DPS ganking mobs from the tank. Ughhhh. I could go on and on about this. But im not.

Personally i dislike almost all melee classes. but thats just me. the reason most people hate them is just because when they first came out they were VERY OP. then they got beat an inch from death with the nerf bat... and now there somewhat OP again. but there ok and i dont usually see to many of them on my server but when there in my raids they dont do TO well in dps tanking there good and pvp there annoying to other people. :P

DK tend to be less... skilled then a player at the same lvl, and most of them use the DK instace gear a bit longer, though i cant really blame em, Blizz refused to make 60-70 Teired armor for em.