when do we bend the rules??

The age old question.
The 1st ט"ז in hilchos נידוי is a shocking one!
the rema there says that if one is חייב בנידוי we do so even if we suspect that he will be "יצא לתרבות רעה" the Gr"a there seems to agree and sites a Gemara in Kidushin 72b as a source. The Ta"z on the other hand disagrees sharply and brings a proof from the Gemara that we must redeem a jew who has been serving as a כומר לע"ז so surely he argues we should בשב ואל תעשה prevent him from going that way. I am not elobarting on the gemaros because you'lle can look it up.
My point being is that according to the Ta"z where does one draw the line, as some בחור asked me, would the Ta"z say the same by מלקות?.