MB3 100b: Saving Someone from Forced Conversion on Shabbos (306:14); Proper Speech on Shabbos (307:1)

Violating Shabbos to prevent an abduction or a forced conversion. Not violating Shabbos to prevent a one-time aveirah.

What kind of matters are appropriate to discuss on Shabbos? Not talking about business or that which is prohibited on Shabbos; minimizing discussion of idle matters.