I see your guys' point, and I agree with you to an extent, but I don't see how bot games are bad for practice. I mean, obviously they're easier. Much easier. I am well aware of how easy bot games are, I hope I'm not giving the impression that I think anything but.
That said, they give you a stress free environment where you can practice last hitting (last hitting is the same no matter how you do it...), figure out builds, and get more comfortable overall with your character. They're also quicker than normals.
If I was serious about League I would agree with you guys, but if I just wanna be good enough to not feed when I'm playing with friends, I don't honestly see the problem with playing a few bot games.