We may not agree on how often being rude is useful.

That is probable. I like to sharpen the point till it gets to be very very sharp. Can lead to bleeding.

in so far as Cochran cares about persuading those who are not yet fully convinced members of Team Cochran, I guess that that sort of rudeness is counterproductive

I don't think he's running a marketing campaign or is attempting to jumpstart a grassroots movement. He's more likely to be raising a flag to see who rallies to it. Or maybe he just likes to grumble and snark :-)