I haven't forgotten the illegal immigration problem, but it is a separate issue in a separate compartment.
Here we have a national emergency and Mexico has sent aid to us. Is it a nominal amount of aid? Maybe. Is it largely symbolic? Maybe. Even if so, symbolism is extremely important.
It is, whatever else might be said, real aid during a time of crisis. They have come to us, bringing help and compassion during our time of need.
How can anyone denigrate that, and why would they?
At a guess I would bet that the people who are denigrating Mexico right now for bringing us aid, are the loudest voices saying that the world doesn't appreciate us when we take aid to them. Look into your own heart and ask if that describes you.
What is it that we want from the world when we help them out? One thing, and one thing only - their appreciation of our efforts. Why then do we not show the appreciation that we often feel is so lacking?