I think you may have a very few in this Forum. These kind of people are very rare.

It's the Moderator's job to return a straying thread back on topic.
The Moderator can not only return the dialog back to topic. S/He can also suggest the digressers either open a new thread on the tangent subject (w/ link from the parent thread) in that forum, or post a link to the new thread, in the more appropriate forum.

Locking a thread punishes the guilty, and the innocent alike.

Why should we reward trolls for allowing them to totally shut down perfectly viable topics, simply by causing mischief?

To me it seems like we infringe the 1st Amendment, for less than a bauble when we do so.

I'm fully aware that "freedom of the press is a right to which anyone with a printing press is entitled".

But I think the soap-box analogy applies here.

The "right" to free speech is empty if we have no "means" to exercise that right.

I realize it's not a dire binary in the broader sense: meaning it's an infringement, not a usurpation.

But why settle for an infringement?
I think RHS' attitude is on target here:
I know of no better way to honor members than to provide for them fora through which they can express themselves, make their case; inquire, inform, persuade, advocate, & debate.

I rather suspect that's the point of this site.

Therefore I believe we shoot ourselves in the foot (metaphorically) to presume nobody will have anything futher to say on an issue.
Thread locking? Bad idea.

One more thing:
It's not uncommon for locked threads to be circumvented by opening a new thread.
The consequence of that is to muzzle the comments posted in the previous, now locked thread.
I have found, generally locked threads are not read as much, if at all. If guests know they can't post there, they're simply not as inclined lurk there.