Why is one unknowable assertion about illigal immigrants valid, and another unknowable assertion about illegal immigrants invalid?

Regarding illegals from Central and South America-

The President says that many of them are hard working people trying to feed their families and get ahead in the world.

This statement is regarded as true, and plus it is Politically Correct.

Donald Trump says that many are criminals and raising the crime rate in America.

This statement is regarded as outrageous, false and plus it is Politically Incorrect.

But the truth is, we really do not know much of anything one way or another about the folks who sneak into the US without real ID or a background check, other than they are here and they broke the law to get here (which may or may not be a clue).

Each statement has an equal chance to be true.

So why is one statement OK and the other not OK.