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.
Exactly like this HN submission did.
Always read the wiki before posting. When in doubt, ask moderators if they're OK with self-promotion.
Self-promotion doesn't mean you spam links left and right. Try to provide value first, and maybe at the end of your post/comment, link to your website.