Earlier quoted context omitted.
The fact that it's a VPN is also pretty important, despite the utility of it also dealing with NAT headaches for you. The main selling point is acting as a relatively efficient private overlay network, giving you a consistent private network even as devices move between different internet connections. (Something that NAT makes a bit harder but you don't get for free even if NAT isn't a factor)
I see it now, it's a bundle of both the practical and security aspects. I think the security aspects serve mostly as a marketing tool, potentially serving users who truly need a VPN. But if I see a user that exposes a server without a dedicated IP address, and they use tailscale for this, the way I would describe it is that they are adding a third party node that routes traffic for them (just to provide multiplexing)…
If you are listening on a public IP, you can trivially be attacked by anyone on the Internet.
If you listen on a private IP that only Tailscale can reach directly, you can only be attacked by Tailscale itself, or by anyone who successfully infiltrated Tailscale's network.
Should you run plaintext protocols over Tailscale? Absolutely not. But you're going to receive orders of magnitude less malicious traffic on a server accessible only over Tailscale compared to a server listening on the public Internet.