No they aren't, some agents have and continue to really help players they represent and also as ( Newcastletiger said I think ) they can really help clubs move on players.
Some though as you say are absolutely awful parasites and it seems to get worse the higher up the pyramid you go
That being said, as a player I'd rather have one then not
As a player I think it's vital to have one or you get taken advantage of by the club you're at. There's a lot players wouldn't understand about the intricacies of the contracts they're signing, and having a club telling them to sign a deal and going along with it can lead to the player getting paid significantly less than they should. Agents do add a lot of value to players, but as supporters of CLUBS we're diametrically opposed to that side of the game and would rather everyone be running around playing for City on 10 quid a week if we could.