Voting in somebody’s primary specifically for the purpose of trying to achieve something that would be universally agreed upon by all real members of the party to be a bad thing, seems to me to be morally equivalent to sneaking into somebody’s house and trying to trash the place - basically, you have to be a scumbag to do it, and it ought to be illegal.
And that applies whether they left the door open, or you had to climb through a window to do it.