You are right.
With a little more education, and a willingness to assimilate and become Americans, many of those coming across the border probably would be good additions to our country. But its impossible to sort the wheat from the chaff, so "Build a Wall, already!"
Part of the problem is that there's less incentive (and it's probably more difficult) to assimilate as the number grows. If you are in a room with 30 people you don't know, by youserlf, you will probably eventually make an effort to meet the other people in the room. If you are in a room with 30 people you don't know and 7 friends, you will probably hang with the folks you know and not make the effort to meet those you don't. It's human nature, stick with what is comfortable and familiar.
Assimilation is the key, and the key to assimilation is biting off smaller chunks. Otherwise, people tend to bring the cultural habits that they left behind right along with them. Some of this is good stuff (foods!) and some of it is not very comopatible with conservative values (corrupt government as the norm, socialism as a way of life). I am frankly disturbed that this seems so difficult for many to grasp.
susie