I know Teemo deserves a lot of hate (uber rage inducing rage of fire)....but, I don't think it's from his shrooms:
1) He is the last attack-speed-hybrid champ, putting him in a unique spot, and making Nashors Tooth not 100% worthless like Tiamat
2) He is the last champion to keep his blind (now that Shaco and Corki lost theirs), messing with the ADC's at late game
3) He is versatile (just not as an ADC or a jungler...both of those are still no-go's), but you can build him as a bruiser, AP bruiser, AS bruiser, AP, tank, split-pusher or a combo of those depending on the enemy comp (I usually go with AP+defense based on the enemy damage sources)
Number 3 is what I think people hate these days....few champions can actually decide to build in a fashion to counter their opponents and still stay relevant. His shrooms are still annoying, not going to deny that (especially when placed well and with 40% cdr)....but the true hate now is the fact that he's one of (or the last?) the few champions that can mix up his build to counter enemies.