How do you know this?
As stated earlier, I remember media coverage of school children and teachers, union members, members of various radical groups, etc. marching in “solidarity.”
At minimum, I think it would be unreasonable to assume that all members of these demonstrations were illegal aliens. While I don’t agree with them, I would assume a great many Hispanic Americans joined in out of ethnic solidarity.
If Linda Chavez, a pretty much down the line conservative previously, could fall prey to the siren call of ethnic solidarity, it is not unreasonable to assume that many other Hispanic Americans did the same.