They were killed by Mexican gang members, many of whom come across the border illegally to sell drugs or purchase weapons.
But the PC side is more worried about alleged "racism" than the actual body count, and ease by which the gangsters sneak into the US
You obviously agree with Trump that these many, many Mexican deaths and disappearances are a "good start" and will cut down on the rapists, murderers, etc. coming into the U.S. illegally from Mexico.
What right-wingers fail to understand is that the tremendous amounts of money made by drug cartels from narcotic sales in the U.S. will not be given up without a fight. .....
I happened to hear Trump give a talk on this matter, and my impression was that he understands the complexity of the entire problem quite well. My impression is that you do not.
However, you are correct that a lot of "right wingers" who think a simple fence would work would line up and support Trump. But that's no reason to think he's got such a viewpoint.