I feel actually guilty when i see obese people...

You know, fat chicks are all the rage in Mauritania, and Tanzania. Seriously beauty is in the eye of the beholder. They look at fat women as hot and sexy.
Anyway, there are much worse things than being fat so I dont mind fat people unless they literally steal food out of my mouth.

No, there's a lot of people with these thoughts. You should look into the fat acceptance movement if you feel this way. You'll learn a lot about the discrimination against fat people. I agree though; people bully and discrimination against fat people all the time, and if they're not doing that, they're making a big deal out of it. I absolutely despise it when an obese person calls themselves fat and then someone says "You're not fat, you're beautiful!" Even if the person who says that has good intentions (they almost always do), when you say things like that, you're implying that being fat is something to have a low self esteem over and that thin is beautiful. I wish people wouldn't make comments about weight or pointed it out because it just does not matter.

First you should not make fun of people
If you can not have any thing nice to say, do not say it

I work with a women that made fun of her little sister for being as size 16. We, a few years later she was a size 16, and she was still making fun of her sister

You need to respect people and you should not say things about anyone you would not say about yourself

As for being fat, there are a lot of happy fat people and a lot of sad thin people. The size of a person does not make the person life better or worst.

I don't get how you can pity perverts and criminals, but I see how you can feel bad for the homeless and others outcasted because of their lifestyles or beliefs.
But honestly the best you can do for them is to be a friend. As for goths, they sort of WANT to be outcasts. That's just part of the scene so they make friends with other goths. If they knew you pitied them, a hardcore goth would cut you. There will always be a place for someone to find comfort (Gays go to the gay bar, Fatties have restuarants or gyms if they're trying to get healthy, Police have the station and their homes with their families, intellects have school clubs and blogs, and goths can just hang out behind the school and smoke) just like how your comfort-zone is probably at the mall or at a nightclub.
Pity isn't helping anyone. It's just making you feel like crap.

I think you are confusing pity with empathy. It's normal to feel empathy towards others, but maybe not so normal for kids and teens because their brains are not fully developed yet and they don't know what the "real world" is like yet. I think you're ahead of the game in that respect. Too bad you couldn't inspire your ignorant friends to show a little empathy for others too.

You're a nice guy, but if you really care about these issues so much, you should start doing something about it. Try volunteering at a homeless shelter or a rehab, for instance.