I hope for you, that you don't SSH into any random machine and just import their cert.

Usually you know the machines you are trying to connect to. That gives you the ability to add their cert to your trusted hosts before connecting the first time. So for browsing the WWW this makes not much sense, since you connect to way too many unknown hosts. It would create a 'red is green' mentality where users just import any unknown cert.

The only similarity i see, which makes sense, would be e-banking and such. The bank could send you their certificate with the login credentials by post.