I think the melting pot is a big part of what made our country great, the best from many cultures became part of the fabric of America. We have one of the most generous immigration policies in the world and we need to keep it that way.
But today's illegal immigrants are different. They don't seem to want to become Americans, they just want what Americans have. Some of the protests awhile back that were shown on the news, they had signs with a map of Mexico, California, Arizona, etc. all combined, some of them actually think they are entitled to take over territory.
Giving the young illegals "papers" puts them in direct competition for jobs, college entrance openings, etc. with "born and raised" American citizens. Not to mention providing a huge incentive for more to sneak in.
The wink, wink, nod, nod that was our border security for all these years is biting us in the butt. One of the biggest failures and mistakes in history for the U.S. government was failing to secure the borders and nip it in the bud before it became so large a problem.