It's not illegal for you to invest in Stripe. It's simply illegal for Stripe to try and sell you their stock. If you happen to have personal connections to Stripe leadership, and they haven't hit the regulatory shareholder limit (after which they must start filing disclosures with the SEC), you could legally buy all the Stripe stock you could afford.
Have you seen an example of a regular middle-class person actually doing this? Because in all the stories I've heard, company leadership just say "no, you need to be an accredited investor to do that", and that's it.
Indeed. In an era where hot tech companies don't go public until they've eclipsed $20B (if ever!), the accredited investor rule feels like the rich & powerful making sure they can keep all of the best opportunities to themselves.
Parents and college buddies, mostly. I've never seen anyone who wasn't personally connected to the founders or VCs be allowed to invest if they weren't an accredited investor because it's simply not worth the hassle to the company.