Good thread, glad we're talking about this again.
Honestly, I'm not just going to sit here and tell you what warrants a down-vote and what doesn't. Ultimately, that's up to you -- you should set your own standard. My best advice is just reserve your vote for the absolute worst, and maybe don't bother on the old stuff that already has 10 up-votes to counteract yours.
When I tell you that phrasing is 'unwelcoming', I don't mean you should start supporting sets you think are bad. I side with you that unknowledgeable content should be criticised. The issue I take with your example is that it's impolite, unconstructive and lacks explanation. It is possible to make a criticism avoiding all three:
Did you create this set with competitive play in mind? It is considered a standard in that format to supply EVs, and to use a boosting nature instead of a neutral one like Docile. Similarly, it's likely not ideal to use Toxic on a Pokemon that is offensively-minded. Maybe consider revising?
The distinction is that you're a) not attacking the person's knowledge of the game, b) explaining why features like Docile are inadequate and c) suggesting or implying what alternative might be ideal. This is actually conducive to a thoughtful dialogue with the author, and all the while contributes extra insight.
This will never happen again. Since 2011, we have had an entirely different standard for voting and for what counts as passable content. Because of that, every moveset thread has multiple years' worth of competent sets that have gone through review. You just have to scroll down or go to the next page to find it.
Sets like the ones you are describing haven't been allowed since PokeBase's first years, and are removed constantly. I take down multiple of the sort every day through the admin. I've also been slowly adding the modern notice about content quality to the old threads, to keep maintenance of this.
As I said in the post linked in the comments, if you're not finding decent content on the moveset threads, you are not looking hard enough. We have acted on this.
For the threads that are backlogged with content from the old days, I do like this idea. I've advocated for it in the past. I don't think it's needed for the Gen 6+ stuff that we handled under movesetbot and the better content policies, but for the 2010 ones I think it's a good solution.
If this was carried out, the old threads would be 'closed', which locks new replies but keeps the thread public. We'd add a notice that new responses belong on the new thread, which would be just like the old one except with better content. We can even update and re-post sets we like from the original.
I don't think it's needed to post something new every generation, but if we do this once, we might consider it again in years' time if a second set of threats meets a similar fate. They shouldn't though, since votes are restricted and quality improved now. New stuff would be much more visible for longer.
If people are posting sets that aren't strategic at all and are just meant to aggravate, then flag them and we will remove them. None of this, however flawless it is:
Metapod @ Hard Stone
Ability: Shed Skin
EVs: 252 Def
If there's at least some effort put into strategy like here and here, I'm fine with it though. (Fair warning, don't click that last one if you don't like racy jokes.)