it hurts my pride, but I'll have to admit that my comment really was more fit as an answer then a comment. Sorry for the fuss, and here is a fitting question if anyone else gets in my situation in the future.
I'm still relatively new to music.stackexchange.com, so I guess I must get the ropes right before anything, but I have a feeling that I've been target of abusive moderator activity.
I commented on that answer about the fact that practicing for the sake of practicing was not very useful on the long run (not exactly those words)
a few minutes later, without so much as a message in inbox which disappeared quickly enough for me not to be able to read it, my comment was gone. Feeling the op, who also happens to be a moderator, had done it I took the time to actually ask him, and it turns he probably deleted it himself, from what he says in comments. He claims the comment was not constructive, I think he disliked it because it contradicted his answer.
Now, he claims that
Comments are for clarity, and are temporary. Where in that statement does it say that moderator can delete comments on their own question without so much as a justification? moreover, he is clearly missing some points on comments:
Comments are often used to ask for clarification on, suggest corrections to and provide meta-information about posts.
my comment provided meta-information about the fact of practicing for the sake of practicing, which is on-topic when commented on an answer which suggest practicing for the sake of practicing.
I can't see the comment anymore, but it did provide factual, arguable information. There was no insult in it. It did not deserved being deleted, it deserved being answered to if someone disagreed.
It would be less of a problem if that moderator actually had real experience in technical violin playing
he claims having played fiddle violin some years ago. Technical difficulty when playing fiddle violin versus classical repertoire is absolutely not the same. My rep may not represent it, but unless he has several years of scholarship in higher education studying the violin, I know advanced violin practice and execution more then he does.
So, can someone with sufficient privileges get that comment here in public and explain to me why/how it was not constructive, as claimed by the moderator who deleted it, if it's possible at all.