Theoretically, those little guys could be the death of all the galaxy if they wished. No conventional weaponry could stop them: even if you brought out your biggest guns, you would only end up shooting yourself with those.
The trial against Kirk and Spock would seem far too limited in scope, really. The whole crew should have been executed on spot for allowing the contact to happen! But how to do that? If the executioner got close enough to our heroes to perform his job, he, too, would be susceptible to Talosian control...
I'd think that, once the contact did happen, the trial from Starfleet's point of view was more or less unnecessary. The deterrent had failed, the damage had been done - it no longer mattered whether Kirk lived or died. But neither Kirk nor (the real) Mendez would know that. None of these people had any idea why the death penalty existed, so they'd go forth with the formalities of the trial anyway.
Spock, of course, would know. And he would also realize that revealing the full evidence would make everybody understand that the death penalty was unnecessary. He did take an awful risk in allowing the Talosians a second try at enslaving mankind - or Vulcankind, considering that he personally probably initiated contact with Talos in order to pull this off. But it turned out all right in the end.
Or did it? It does sound like the Talosians finally got the breeding pair they wanted. The rest of mankind might be safe now, but there would still exist a slave caste of human beings on Talos. Unless the combined effect of and Pike's injuries was enough to prevent procreation, that is.
Timo Saloniemi