There's a difference between diehards and politically naive/illiterate/stupid. Though whether it's worth targeting the latter group is debatable - how much time/effort/money for how large a group and all that.
I think what isn't debatable in this line of conversation is that knowing how to deal with the diehards - knowing how to spin a narrative that shuts them up, makes them feel stupid, makes them feel embarrassed to raise Trump with their friends/relatives/coworkers - is something that's needed. Control the narrative enough that you shut-down the diehard's easy comebacks, and you have a more manageable situation. For example, saying to someone who's wearing a "Grope This" shirt that someone you know was raped/sexually assaulted means they can't (easily) say that "It's just locker-room talk". They can still argue the point, sure, but at that point they come across as awful human beings, especially if you're a "normal looking" white guy, middle-aged/old. Trump supporters thrive on the perception that they're normal, and everyone else is "wrong" in some way - if you come across as just as normal as they are, they have less to work with.