Anybody who gives the slightest fuck about finding an alternative is already aware of kbin/Lemmy.

That's just empirically not true and it's not how people and internet communities work. But I guess a more important question is, are you saying this because you believe it to be true or because you are happy with the size Kbin and Lemmy currently are and would prefer not to have a mass migration from Reddit that would change the vibes ? Because that's absolutely a valid concern. If that's not where you're coming from and you really do just think that sentence is true, at what point in time would you say we reached the point where everyone who needs to be aware of kbin/Lemmy became aware of kbin/Lemmy?

By trying to “advertise”, you’re only opening up the platform to brigading.

You WISH kbin or Lemmy were big and well-known enough to be worth brigading. Or maybe you don't, which would be valid as I said above and is a different conversation. And it's possible that by "brigading" you mean "an influx of newbies who ruin the vibe", in which case I agree that this is a possible effect of what I suggest. In fact it's the desired effect. However if this does in fact result in a mass of people going onto the platform with the intention of ruining conversations who would not have gone on it instead, that would suck but I'm not sure it couldn't also be leveraged as a streisand effect. Kind of like how for a nobody like Rocky Balboa just being in the ring with Apollo Creed was a win.

Oh, and on top of that, you’re giving Reddit additional traffic, which is exactly what they want right now. Just leave it alone!!

Yes, giving Reddit additional traffic sucks and is what they want. If there were a way of participating in r/places without doing so I'd recommend that as a no-brainer. However it doesn't just give Reddit additional traffic and "what Reddit wants" isn't necessarily what's actually best for Reddit. I made an argument for why I think it would also cause a certain amount of migration from Reddit and we can get more into it once I better understand whether that's something you want to avoid or not. The question then becomes what the net effect will be, and I don't think that's easy for anyone to know, including Reddit. But numbers-wise, given the number of people in these threads compared to the audience of r/places and the percentage of that audience who would be nudged towards checking out/contributing more to kbin or lemmy from seeing them on r/places, I really feel the net effect is more likely to be on our side.