Do you see any differences between those two types of arguments? I see differences, and to me they are important. Type C arguments are about the consequences of policies. Type M arguments are about the alleged motives of individuals who advocate policies.
His point hits close to home for me. One thing is that type M arguments are useful when you’re preaching to the converted, whereas type C arguments are useful for debating the issues with people who don’t necessarily agree with you. I try not to make or link to pieces that rely on type M, but I’m sure I fail (probably all the time). Anyway, it’s something to keep in mind.
By the way, Arnold Kling has a weblog. So you can see whether he lives up to his C over M expectations.