I've found this to be the case also. It's so heavily gated that there's almost no point in bringing up a new project or tool because it will be batted down if I'm the one that wrote it.

HN doesn't have that auto-gatekeeping but has taught me to really soft pedal posts about my own stuff. When I've managed to present it as a useful thing and not just my thing, I've gotten significant and sustained lift here.

I don't see this as a problem. We have a marketplace of marketplaces of ideas - yes, Reddit is a big one, but there's HN, Lobste.rs, even slashdot is still alive and functioning. If rigid bans on self-promotion are harmful, Reddit will die and more marketplaces of ideas will spring up to take it's place, like blades of grass on the prairie. We don't need every single social network to become an outlet for startup self-promotion.