antinatalism is depression turned into a moral philosophy

Not necessarily. Antinatalism and other pessimistic points of view can be held by non-depressed people. On the internet, it seems like psychological pessimism is the same as philosophical pessimism as many depressed people do adopt these points of view and flood the forums. Adding to that, they often abandon their philosophical pessimism when their depression lifts, leaving a testimony that it is true: only depressed people defend these ideas. But we need only an example of a person that is not depressed and still values antinatalism on its own to demonstrate that your statement is not the case, and I think I might be that example. Many other examples might be found in universities. I hope one day we get a formal social study so that I do not have to give anecdotal "evidence" and personal information.

Now, I'd add to defend those I know that are indeed depressed, we should be debating and trying to refute the philosophy itself. Even if depression is leading them into these kinds of thoughts, we cannot say that this disproves their ideas. Many brilliant discoveries and inventions were reached in what we classify as pathological states. The manic researcher and crafter is an archetype for a reason (e.g., mad scientist, mad artist), and we have not fewer examples of depressed people that made valuable work, such as author F. Dostoevsky. There are two books that are coming to my mind that explain why (specifically) mood disorders are pathological but still let people do great things: A First-Rate Madness: Uncovering the Links Between Leadership and Mental Illnesses and Touched with Fire: Manic-Depressive Illness and the Artistic Temperament. So, as I was saying, the fact that someone is clinically depressed does not inform us about how true or how solid their ideas might be. Discrediting them just because they suffer from depression would be an ad hominem, and, in the moral part, ableism. We need to listen to/read their ideas and discuss the ideas instead.

it posits itself as a solution to suffering by offering an unrealizable future

This is a very misunderstood part of antinatalism. Almost no antinatalist is utopic in their views, that is, few antinatalists think that the point must be to cease all reproduction and that antinatalism fails if they don't. That would be an ideal scenario; there's no suffering without existence, but that is a dream. There are no goals for many antinatalists, just the idea that bringing children into this world is not ethically correct. They might follow antinatalism and not have children or adopt, but not preach much about it because they know practically no one will listen. I, for instance, bring this problem to people that might have not thought about it before. If they go ahead and have children, I'd still think that was not correct, but well, nothing to do but to help take care of this new life. It can be as pragmatic as that.

but really it's an excuse to not even attempt to make the world better.

No. In my case, I try to help in other ways. This right here is an example as I'm trying to broaden the discussion around these topics in a healthy way because I know Reddit has sadly damaged these debates with a lot of insults and bad attitudes from many sides. They insult people, so these people go to their subreddit and insult them back... It is not a good way to first learn about these topics, and many are learning what antinatalism is first on Reddit. I hope Lemmy will be slightly better.

Anyway, I also try to better the world in the ways I can. Still, as a person that values philosophical pessimism, I think we are only saving lives from a neverending fire, or giving palliatives for an incurable disease. I enjoy my life and I try to help others enjoy theirs as much as this existence lets us.

If anything, philosophies around negative utilitarianism, preference utilitarianism, overall pessimism, etc. tend to respect others a lot and value their suffering negatively. That's usually their point. Suffering is not a "necessary side for pleasure" or "a trial from which we gain something" or "something not that bad" or any explanation different cultures have given. Suffering is bad; in a better world, it wouldn't exist like this. It is tragic, but it is reality, so we must face it and combat suffering as best as we can. I'd say these ethical paths inspire protection of others more than others less centered on sentience.

Finally, it is good advice to seek professional help, but not on the sole basis of someone being an antinatalist. If our OP here is depressed, I do recommend visiting a professional.