As of yet, Trump has taken no concrete action against either Mexicans or Muslims, for the simple reason that he is unable to do so with any kind of effectiveness. Is a preemptive strike against somebody who has done nothing except make abhorrent statements justified or practical?
Yes. It is better to defeat your enemy before they can inflict damage, than to wait until the damage has already been done to attack. In addition, it is a far easier objective to try to prevent him from becoming president than to try to stop anything he does once he is already president. The common people cannot influence Capitol Hill, nor can they storm the White House. Now is the time to attack Trump.
I'm not a fan of Donald Trump, but if you go to his rallies and assault his supporters, you are part of the problem. Simple as that. Not only does this just make him more popular, but more important, it violates his supporters' basic human rights to freedom of speech, assembly, and association. You want to stop Trump? That's fine, so do I. But there are far, far better ways of doing so. Find a method that doesn't hurt innocent people or make it look like he has a point.