Almost true. In most cases of stalking, you're right, because there is no evidence of mental illness.
To your point--no psychiatrist will institutionalize someone on your testimony, but a judge might. Depending on the state, a judge can send a person on a 72-hour court order to a psychiatric facility on the basis of an affidavit from a concerned party. If you can convince the judge, which in my state is apparently not difficult, the person wins a psychiatric admission.
I would receive advice from someone who has dealt with these issues before even thinking about such a course of advice.
"Lock em up!" feels like a great idea. Until you wonder what happens between them hearing about it, and showing up in court. Or after they are released from the psychiatric admission.
> No legal procedures exist to put down a stalker until after an actual crime has been committed.
That's not really true without jurisdiction filter on the assertion: there are jurisdictions in which harassment itself is a crime (in all circumstances, not just for protected categories or e.g. in the workplace). For instance, the UK with the Protection from Harassment Act 1997.
No legal procedures exist to put down a stalker until after an actual crime has been committed. Really, really, REALLY liking someone is not a crime.