why do ppl laugh at other`s english?

i know there are so many ppl out here wanting to learn english...

and the key to succeed is not to be shy and be brave to speak out

even though i know my english is not perfect or say "good"

but it is also a way of practicing my english (my reason for often typing english is becos every time when i type in chinese, my pc automatically shut down)

so.........i am also kind of forced to type and communicate in english over the net

however, i dont understand why, sometimes, ppl would attack others for not being able to communicate in perfect english with others

, sometimes, in some other threads, they would encourage ppl who want to learn english be brave to use english at any time...

i think it is contradictory, and it also lets me fear to speak out in some threads...........