why are people like "u r dumb" so rude to people...kindness goes along ways?

Answer 1

some people seem to feel being perceived as 'kind' is a weakness. That if you demonstrate kindness in words or deeds that you are somehow being 'fake' or not being yourself. I don't understand that reasoning.
A lot of people try to impress their peers when they're in a large group, by copying their behaviour. Everyone wants to fit in, to belong, and so if you choose a group of people to 'fit in' with and they act unkindly or without any responsibilty towards others, then you have to assume these traits to carry on 'fitting in'.
A person with a moral conscience will eventually realise they are not being true to themselves and move away from this social circle. Sadly, others who are impressionable carry on following this behaviour, and in time it becomes second nature to be rude and unkind.

Answer 2

What, with a screen name like "u r dumb", you think that he/she is going to be helpful and and kind?

You are right, kindness does go a long way, but some people never find that out.

Answer 3

People, especially in the internet, like to feel superior to others.It could be because of an age difference between the asker, and the person that answers, spelling mistakes, and so on.