Playing devil's advocate encourages terrible thinking and using arguments as soldiers.

I come to the exact opposite conclusion. It's certainly possible to be a poor Devil's Advocate: an easy way is choosing poor, unconvincing, arguments. But the exercise of trying to make the most serious and plausible argument for the other side involves carefully examining the opposing arguments and evidence, and taking them seriously, rather than as enemy soldiers to be shot down. A good Devil's Advocate learns to judge arguments and weight them based on how useful and effective they are, how convincing they are to the unaligned. While not the same thing as "how true they are", it is a serious step up from "how much of a security blanket they are to the unconvinced", and much more likely to lead to "how true is this", especially in the context of rational unaligned third parties, where truth is actually a strong element of convincing.