> If I can't post my FOSS to the linux subreddit then what in the world am I allowed to post?

There is not enough information in your comment to judge correctly, but I would like to point out that it's not black and white.

You know what I hate about Hacker News lately? The green accounts that show up, post a link to their product (sometimes even making it to the front page), do not reply to comments, and exist only to keep spamming their own links. I also saw a post gain 16 upvotes even though they forgot to post the actual content.

If you regularly contribute to the linux subreddit, participate in discussions, and post interesting links from non-affiliated sources then yes, being deleted for "self promotion" sounds unfair. But if you only go there to promote your project then I'd also side with the mods.