During The Troubles bombs were sent via the Royal Mail. Nobody blamed the post office. Indeed any infrastructure is a tool of terrorism as we rely on it (I am not going to make a list for obvious reasons). I think the reason we tolerate this problem with infrastructure is that the benefits outweigh the risk. The question is whether or not the same applies to free speech - you're right there is no win-win solution, but it still might be worth it.
However if you start "Peters no questions asked hand delivery service, shipping direct from Ireland to London so reliably you can set a timer by it" - and you deliver 3 bombs to politicians you might find yourself being asked a few questions.
At the time that's exactly what the Royal Mail was. Requiring identification to send packages is a much more recent development. Society just accepted that bad actors could do this and solved the root problem instead.
There are quite a bit of differences here. The mail services transport physical goods, and the whole path can be tracked. Every letter or parcel is registered by the postal office where it was submitted to for transport. And usually there is quite some physical evidence with everything you do mail.
> I think the reason we tolerate this problem with infrastructure is that the benefits outweigh the risk.
The thing is, we absolutely don't tolerate this with infrastructure. We have entire systems in place to make sure that we can find people who use our infrastructure to kill people. The USPS has its own entire law enforcement branch whose sole job is to track down people who misuse the mail. I'm sure there are processes in the UK for the same.
With our infrastructure there's some non-zero amount of abuse that we acknowledge we won't be able to prevent in order to make everything work without infinite enforcement cost, but we don't just close our eyes to the abuse and not even try to do anything about it at all.
The difference between the post office and Tor is that Tor is very specifically designed to make tracking a sender of a bomb threat impossible. State-run postal services at least try to have an audit trail for what they send.
