Coming from Florida, we have huge immigration issues with people from Latin America. The problem is that massive amounts of people come into the state and automatically get social benefits. They can attend schools, use medical facilities and receive government assistance. They pay no taxes, so it is the American taxpayer that has to pay for them. People don't (in general) dislike people coming to the US who contribute to society, they don't want people who instantly drain the welfare system.

Note about schools: the US school system is set up so that anyone can register their kids for school regardless of who you are or you status in the country. No address? Your kid is just listed as homeless on the record books. We actually had a large number of British folks who would come to the east coast of Florida on holiday and register their kids in the local schools so they had an option on days when they needed a place for the kids to go. Absolutely true story. No one can be denied education.