It's a fact that makes people uncomfortable. Similar to facts like "women on average have less muscle mass than men." And I think you'd agree that people from the right would jump on someone who disputed the muscle mass fact as "out-of-control political correctness."
There are facts and there are non-facts. That women have less muscle mass on average is a fact. "Mexico sends their rapists" is not a fact.
"When Mexico sends its people, they're not sending their best. They're not sending you. They're not sending you. They're sending people that have lots of problems, and they're bringing those problems with us. They're bringing drugs. They're bringing crime. They're rapists. And some, I assume, are good people."
You have no idea what you are talking about if you think this point is disputed by any majority of Republicans.
It's like saying, "'People should contribute to society' triggers all liberals."