I've noticed that when people complain about racism in a context like this, they end up sounding way more racist than the thing they're complaining about. The way they're getting upset about mariachi Mario makes it seem like they think that sombreros and mariachi are a negative representation of Mexican culture. In reality, sombreros and mariachi music are fucking badass.
Fuck, I remember having an argument with someone who thought that just saying "Mexican" was racist. He understood that you aren't supposed to say all brown people are Mexicans, but somehow he decided the word itself was racist. If you think that calling someone Mexican is a horrible insult, you probably don't think very highly of Mexicans.
So in conclusion all these people hate Mexicans.