It's probably a good mental discipline to go through this process in your own head, to check that you're not firing off an unwarranted accusation, but sometimes it really is pretty obvious that a particular error has been committed, and in such cases the shorthand seems both useful and justified.

It is really easy to give yourself too much slack when checking these things in your own head. Actually committing your justification to a public comment that others can scrutinize helps to honestly evaluate your own position.

Further, though it can be reasonable to present a position without support when no disagreement is expected, in the case of a counterargument, there is already disagreement, which you should attempt to resolve by presenting your actual reasons for holding your position.

If it's still unclear to others, I'm fairly sure someone will come forward and say so (and they should be encouraged to do so).

A large part of my motivation for this post was to encourage this behavior.