Is the failure to invite people of innovation to the truth considered a sin, and is the ignorant person excused for that?

Calling the people of innovation (Ahl al-Bid'ah) to the truth is obligatory upon one who has knowledge of it, is capable of debating them, and is safe from being affected by their specious arguments. As for the ignorant, he must first learn. Regarding the bigoted among them, who do not accept the truth, the ruling on calling them branches out from the scholarly disagreement concerning the obligation of enjoining what is right and forbidding what is wrong (al-amr bi al-ma'ruf wa al-nahy 'an al-munkar): Is it conditioned upon people's acceptance or not? A group of scholars has favored its obligation even if no benefit is known to result from it.