I don’t go looking to pick fights, but I’m not going to be a wallflower anymore; when I see people attacking the Church, I’ll take them on. And I’m going to use their own tactics against them, because it drives them absolutely nuts to have their own attacks turned against them.
Example: When some nasty anti-Catholic insists that Jesus didn’t want us to follow any Church, I just point them to Matthew 16:18 and Matthew 18:17, then suggest they should start reading the Bible instead of worshiping it. For some reason, they don’t like that one.
As for the OP, many Protestants are willing to go along to get along and aren’t interested in fighting; they are great to have discussions with, because they aren’t shutting down any dissent from their pre-existing opinions. Those ones, I have no problem with and get along fine with. But the others…
My admittedly amateur opinion is that many of them have invested themselves totally in what they think the Bible means, and they simply can’t accept the notion that they could be wrong. And so whenever they see anything that challenges that world-view, they lash out, much like liberals after November 8th last year. Some of them are honestly trying to save souls (in their own misguided way), but a lot of them just want to vent their hatred of anything Catholic. Many of them are ex-Catholics themselves, trying to justify their apostasy.
There’s not much you can do to persuade them that they are wrong; you’d have an easier time convincing a Muslim or Jew to eat a ham sandwich. So for my part, I just have fun with them, turning their own arguments against them and dropping barrels of scriptural references that explicitly deny whatever they are claiming. If you do it right, it can be very entertaining; I actually got one of them so discombobulated that he finally made the claim that some of the Scriptures are NOT actually inspired (he couldn’t handle Peter’s statement that Baptism saves us, so clearly it wasn’t inspired).