Well, I'd admit, Luther had a sharp tongue. But also be somewhat understanding of who he is in his context. Here all these devilish papists, worms who have deceived millions of people of hundreds of years with their popery over the simple truth of the gospel and they've made it all about paying money to these guys going around to build St. Peters. So there's only one church at the time (excluding the wacky Eastern Orthodox for the moment), and the only church to belong to is the RCC. And God's people within her mostly all have been deceived by false teachers. Now, as a Pastor, I would be angry. Just as Christ was, and when the Jews were desecrating the Temple, and He went in and turned over tables and took a whip and was using the whip to get people out of the temple. I see a good deal of that in Luther. Maybe not all of it was righteous, but I think it at least stems from that and so he's attacking these false teachers (e.g. Erasmus). So that's why it is my view you should give him a little slack, and just focus on the arguments he makes.
Besides if we criticize Luther (which is all well and good), that doesn't mean we dismiss what he's said. If we did that, then we would have to dismiss all the writings of sinners, which is all but what we find in Scripture.