> I know some actual users get blocked. But the amount of spam we get without it, the amount of bot traffic simply overwhelming the server... It is just too much.

So why not just shut down the website? Or remove the form entirely? That will ensure that you get no spam, right?

One of the core tenets of system design is Availability. If your service is not available - if your forms are blocking legitimate users - then why are you pretending to have a form submission feature at all? Just to frustrate users?