Rhetoric skills are like a knife: If you have a knife, you can use it to kill people or you can use it to prevent people from being killed, but possessing it will not kill you, with admitted rare exceptions.

The analogy is not a useful one. In this context it is the killing that is desirable while the use of the knife is the problem. I would prefer people didn't believe stupid things. All else being equal I would prefer to not rely on the exploitation of cognitive biases and weaknesses in reasoning in order to do so. There are cases where this is useful.

When I suggested 'let them debate college students that we weren't expecting to actually think rationally anyway' I mean just that. Most people, even most scientifically minded people, I expect to arrive at accurate conclusions through the social pressure of the institutions we have in place rather than actual rational thinking. With those people by all means throw them out to play word games with crackpots if it benefits whatever cause is valued. But for myself I know that the better I become at arguing with rhetorical tricks the more likely I am to stick to false conclusions.