Why are people so mean to immigrants?

I've been to those 3rd world countries where immigrants come from and I understand why they move yet people who are priviledged to be born in a place where they have opportunities just insult them and want them to go back to a life of poverty and a life where no matter how much talent, skills and even qualifications they can amount to nothing. I think it is selfish when people say 'Oh send them back cos they're not from here' as anyone in those immigrants shoes would do the same to escape death or to just find a better life for themselves. Now of course I don't condone immigrants who just come for the benefits of sell weed and all that but for someone like this guy, the comments people wrote on his case is sickening to be honest.a href="http://www.dailymail.co.uk/news/article-1296762/Iraqi-boy-studying-GCSEs-thrown-Britain-experts-say-youre-20-years-old.html" rel="nofollow"http://www.dailymail.co.uk/news/article-…/a All he is doing is trying to be a normal boy after all the trauma he's faced.