Very true.  Trump has the right and freedom to speak.   But the 1st Amendment applies to everyone equally.   So Trump protesters have the right to speak their minds too.   And if they want to yell and drown Trump out, that is their right to disrupt his rally.

My prediction: There will 4 Trump protesters for every Trump supporter at the rally.   The crowd will be so very hostile to him, that Trump will end up being publicly humiliated.