It's not unilateral at all. Sites have a choice if they offer connections over https, it's far from universal. By accepting http connections the site has indeed notified the browser that it wants to only allow secure connections. The problem is that a browser is refusing to connect to a server that has declared that it requires security but that it can't connect to because the browser has implemented it correctly and the server hasn't. It doesn't matter if that's temporary or not, the message of "I need a secure connection" has been understood.
Perhaps the browser should have a fall-back to http button, in which case the server's choice of how to redirect to https will be the deciding factor. I doubt many users routinely type https:// to signify that it's their wish to only have a secure connection, so in this case it is certainly the server that's enforcing it.
We need to move to TLS by default with no unencrypted HTTP, that can allow old crypto and unverified certificates. That will turn http into kinda-secure http but not compromise on the security of sites that have specifically declared themselves as wanting to support only secure connections.
