>open to all

That's in direct opposition to security. When you grant people you don't even know much less trust access to your system, all bets are off. There's just no way to predict what is going to happen. You've lost the fundamental protection afforded by trust.

Today, computers are expected to be able to talk to and serve hundreds of thousands of random users. What if one of them has access to a 0day? They could own the machine. The world would be a lot more secure if servers dropped all incoming packets by default and talked to trusted users only.

Bitcoin is open to everyone and that's great, but it doesn't change the fact people managed to sneak a bunch of illegal pictures into its blockchain.