Let's put it this way:

At least FlatAssembler is enrolled in the class, while you're some random stranger throwing rocks in the window.

As for contribution, what I meant was that you could do something other than complain about the ideas others suggest.

That was a metaphor, of course. What I am saying is clear: he is interested in and aware of general theories in Linguistics. You do not seem to be.

Compare this to learning mathematics: he seems to be trying to understand how math works (and potentially make a contribution) while you are just saying "math is stupid! I don't believe in numbers!" It's tiring, and pointless.

Even if FlatAssembler is wrong, that's like getting a math problem on homework wrong. That is: at least he's trying to learn, and he is doing it within the normal methodology of linguistics. Maybe right, maybe wrong.

Overall, you're mixing up two things:
1) Whether or not FlatAssembler is correct.
2) Whether general theories in linguistics are valid.

If FlatAssembler makes a mistake, that does not mean Proto-Indo-European is an invalid hypothesis.

It is incredibly frustrating and repetitive trying to explain this to you. We have both clearly wasted enough time on the conversation. If you say "I don't believe in numbers", then I'll tell you: "Then don't do math." And that's where things seem to be about Linguistics.

FlatAssembler is doing Linguistics. (Maybe right, maybe wrong.) You are not.

Social sciences don't appear to be real sciences. Trusting the mainstream social sciences has brought us things such as socialism and communism. Seems to me that I am better off thinking with my own head than trusting you guys.

Nonsense, but OK. Yes, please, go away.

First they deny the obvious fact that Croatian and Serbian are the same language. They say they are "closely related Slavic languages".

That isn't a substantial distinction. So what if they're languages or dialects, and how would it relate to the question here?

Then FlatAssembler goes as far as saying that the Croatian toponyms aren't Slavic, but come from some unattested language. The amount of mental gymnastics it takes to invent a whole language, completely different from Croatian, from which the Croatian toponyms supposedly come, is impressive.

There's nothing particularly unusual about toponyms coming from an earlier language. An obvious example is all of the Celtic place names in the British Isles, despite English being dominant today. That may seem less unlikely given that Celtic is attested, but surely something was spoken in Croatia before Croatian (say, 2000 years ago). This isn't in defense of FlatAssembler's proposal, but your counterargument is not evidence against it either.

As with the rest of the discussion above, none of this seems to really connect to the etymological details of the proposal, so I'm not sure the debate needs to be opened back up at this point. As I've said, Croatian toponyms require quite a bit of expertise in specific areas to discuss in any detail, some of which seems to be beyond this entire discussion as a whole. All I can really say is that at least FlatAssembler is trying to get there by talking about the details of etymology. Maybe there's not right, but the counterarguments are not convincing either.

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BTW, why the hell did it take this forum more than a day to send me an activation e-mail so that I can post here?

Not sure about that. But my guess is that it isn't on the forum end of things-- the forum software isn't designed to "save up" emails in a queue to send at some indefinite later time. It would be processed automatically when you submit your registration. So it could be delayed somewhere on a mailserver 'in transit'. (Maybe there's a queue in the mailserver for the forum, or maybe in your email receiving it.) Anyway, welcome.

You think that just because you know some linguistics (whatever that actually meant), you can evaluate theories about Croatian history?

No, I can't. That's what I've said here. The details are beyond my evaluation because it requires a lot of knowledge of specific subfields. And it's not just knowledge of Croatian, no.
(As for Serbian/Croatian politics, I have no interest in discussing that here, because it has nothing to do with linguistics.)

Because many of the toponyms he cites are perfectly explicable using it. The name of the river Vuka, for instance, obviously comes from the common Serbian personal name Vuk.

That's possible. But sounding alike doesn't mean the same etymology. And that's what I've been telling FlatAssembler, if you read the posts above (skipping over the tangents). Etymologies are very hard to prove beyond a reasonable doubt, if there are other plausible competing theories.

He just doesn't want to admit that it's Serbian and therefore that it should belong to Serbia.

OK, so that's you making this political. I don't know if FlatAssembler has a political motivation. Maybe he does. But he hasn't made any arguments based on that, and you just did. No place "belongs" to any political entity because of the language that is spoken there. That's not how politics, or linguistics, or life or the world works.

This has nothing to do with linguistics, this has to do with politics.

Indeed, nothing you have said is about linguistics.