There is no moderator abuse here. Dave acted reasonably and correctly. Another possible mod action might be to delete the whole chain of comments. The basic problem is that you misunderstand how this site works.
You have a number of times now tried to use the comments to debate answers. If you think an answer is wrong, misleading, or badly written, it is fine to state what you think is wrong and downvote. If you think you have a better answer, write one. Note, of course, that others may downvote your answer if they think it is wrong, misleading, or badly written. Hopefully they will do you the courtesey of telling you why.
However, comments are not for picking on what other people have said to try to tear them down, be contrary, engage in a long debate, or just whine. If someone else's answer isn't really wrong, but you think it's not to the point, misses something, or generally could be better, go write your own answer. Think of it as an opportunity. If the other answer really does miss the point, you'll be the hero with the most upvoted and accepted answer. Other than outright errors, misleading wording so that others are likely to interpret something incorrectly, or really bad writing, let the multiple answers and voting system sort things out. That's what it's for. That's how this site works.
The Specific Complaint
You have taken Dave's comment out of context. It was clearly in exasperation to your previous comments, especially the previous one:
@Dave Tweed: I'm constantly amazed at the arrogance of you people, who consistently come up with: "What the querent wants is unimportant, what we decide to give him is what matters." Olin's attitude is particularly egregious because he actively tries to scare away those who aren't interested in jousting by making their retaliation onerous and then, when silence ensues, damning the querent because of his silence. That's a horrible way to treat people who are asking for help the best way they know how, and doing it by sharing their thoughts.
This simply doesn't belong in a comment. It wasn't even commenting on the answer as much as reacting to another comment from Dave where he tells the OP to not presuppose a solution.
Aside about OPs asking about particular solutions
OPs pre-supposing solutions is rather common here. This case is as good an illustration of this as any. The OP wanted to know how to amplify a sine wave produced by a microcontroller to a line power signal. Quite possibly, all he really wants is the line power signal, especially since he specified it as 220 V 50 Hz. He is imagining starting with a small sine wave, then amplifying it to produce the final output. Telling him there are such things as inverters and that they work by synthesizing the signal implicitly by controlling the switches each pulse could be useful. You are right in that he might actually have a different case where the desired output is not just line power, but that doesn't make mentioning inverters a bad answer.
There is also nothing wrong, in fact it's often necessary, to ask the OP for more detail. Originally this question didn't even mention what the output voltage and current needed to be, and could possibly have been answered with a small opamp circuit. Only when he mentioned (even though he commented that it was unnecessary to supply such detail) that the output was 220 V at 2.5 kW could a answer be attempted at all. Unfortunately he never did answer what the nature of the input power to this amplifier was, nor clarify how the output power was to be used. If he had done that, a more targeted and useful answer could have been written.
Asking for more information and/or asking the OP to step back and explain the larger problem are useful and all too often necessary things to do. Complaining about someone else asking these things is inappropriate. If you think you have the answer without requiring additional information, write it. However, if you have to make assumptions to sensibly answer a vague question, be sure to state your assumptions. Without that, a specific answer to a general question is wrong and others may downvote your answer as a result. If you state the assumptions, at least the answer is correct, even if it turns out later to not apply to what the OP was trying to ask. I wouldn't downvote such a answer because it is at least self-consistent and correct within its defined scope. Put another way, answers to questions with vague scope must be either vague themselves or define their own scope.
In this example, if you really were so sure that the OP needed to amplify a arbitrary signal to 220 V at 2.5 kW and you felt my answer was missing the point, the correct action would have been to write your own answer, clearly stating that it applies to amplifying an existing arbitrary waveform. It would be good, although not necessary, to mention that if the desired result actually was just to make line power, that there are more efficient solutions than starting with the output wave shape and amplifying it. I may not agree with your premise about what the OP really wanted, but I wouldn't downvote it, as long as you stated whatever assumptions you made about interpreting the question more specifically than it was written.
You have now a number of times tried to tear down other people's answers, particularly mine it seems. Often these comments have been about meta issues and not about the answer or the question. This is not appropriate and has to stop. Comments are not for berating other people about asking for more information, or telling them how awful they are for daring to give a alternative answer to a different interpretation of a vague question or one that pre-supposes an inappropriate solution. Again, if you think you can answer better, go answer better.
Stop trying to tear down others just because you disagree with their methods. The place for that is meta, not in the middle of a technical question and its answers.