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.

...sometimes it really is pretty obvious that a particular error has been committed...

I favor more detail over less. Obviousness isn't an intrinsic characteristic of an error -- the danger of not spelling something out is a miscommunication due to typical-mind-type hidden assumptions (on the part of either person in the conversation). The key is to keep the level of detail below the "excruciating" threshold.

Assuming your primary goal is to communicate the error then being able to communicate the reasons for the classification of the error to yourself may be of some use, but that is not equivalent to successfully communicating the reasoning to the person who has committed the error.

On the other hand, if your primary goal is to signal status, then inconspicuously failing to communicate your reasons is good, as long as others do not point out your own errors. Which makes self-checking closer to sufficient.

Admittedly, that doesn't mean that this post's obligatory explianation is the best way to communicate reasoning either. Reliably successful communication is a hard problem, which means applying serious rationality to it.

sometimes it really is pretty obvious that a particular error has been committed

The degree or lack of obviousness is a fact about the reader's mind, not about the error.