There are often times where I have no interest in discussing a particular topic, and yes, I will put my foot down if someone tries to push it. There are also times when I'm in conflict with someone, but my emotions are too strong so I cannot discuss it with them rationally. So I will also keep my boundary and say I cannot discuss it right now, but in those situations, the fair way to deal with it is to let them know you will discuss it tomorrow or when, because it's not fair "fighting" when in conflict with a loved one to make them wait forever to resolve a conflict. People have the right to cool off and get their emotions in check before they discuss with you.

I'd say I need to know more about the context of when people are refusing to discuss something with you to know if there's anything to be done about it.