Why do people say bad things about anime without actually watching it?

People just like to judge books by their covers, no matter how many motivational posters my school puts up about not doing that it's still going to happen :/ It's easier to just say no I hate it then to take the time to actually see what it is. Granted their are many people who like trying new things and are willing to give things a try, even so they may just not like it. Weather it be the art style, not finding a series that interests them early on, I know people who just plain don't like watching animated things they prefer live people. I think specifically anime also has a stigma to it, it's associated with your classic shut-away nerd. People being the people they are don't want to be associated with things they believe will make them look bad.

seeing cartoons like tom and jerry and mickey mouse they start to think that every thing thats not real, like anime are childish and non serious like the cartoons but actually theres a huge difference between both anime can be more serious and mature than the real and can perform things which the real people cannot which makes it even more interesting...

If you're talking about specific shows... I do that on occasion and I don't think it's stupid or anything to make a judgement about something you haven't seen if you know enough about it to know that you think it's horrible.
If that makes sense....

It's a shame really... they judge it without even knowing what it is. Take it from me, I use to think anime was weird without even knowing anything about it. It was a weird Japanese thing and characters with big eyes and colored hair. First thing that came to my mind is porn or Naruto. I was pretty was bias. My friends are anime fans and introduced it to me. At first I would think they're weird when they would watch it. Then, however, I became addicted myself. So when someone says "I hate anime" or "anime is weird", I ask them how much did you actually watch? Or "I used think that to until I ACTUALLY WATCHED it!" anime kind of has a bad rep and labeled as "porn" or "cartoons." Some people can't see anything animated being mature, sad really :( they just don't know what the're missing out on.

Well... they see shitty anime first and judge all anime based on that.

That, and... those type of people find both anime/cartoons childish. Anything can be immature, though, just as anything can be mature.

There aren't very many mature adult themed anime shows (N.o.t. talking about hentai/ecchi/yaoi/yuri), but rather, seinen and whatnot... so maybe that's why some people don't like anime or quit liking it after a while. A lot of typical anime seems to be mostly about school... and that's really boring. xD

Part of the reason is probably because they grew up with dubbed children's anime shows for their usual Saturday cartoons and now think all anime is childish.

They say bad things about anime because we talk about it too much. When we talk about it around other people who don't understand it they say it's stupid and we shouldn't watch it. But once they find an anime that they like they fall in love and continue to watch anime. My sisters were like that but once they saw one episode of Fairy Tail they loved it.