Ibn Taymiah (r) said:
“It is an obligation to punish all those who originate to them (oppressors, innovators and people of desires) or defends them or praise them or praises their books or is known to help them or support them or dislikes speech against them or makes excuse for them like ‘we don’t know what this speech of theirs really means’ or one who says: “did he really write this book?” and other similar excuses which no one but a jahil (ignorant) or hypocrite would make.
Rather it is an obligation to punish all those who know their condition but do not aid in refuting them. Because refuting them is from the greatest of obligations. Because they corrupt the intellect and religion of the elders, scholars, kings and leaders and they spread corruption in the earth and they block the paths leading to Allah.”
Majmoo al Fatawaa V2/P132
I say this punishment can only be exercised by a leader who has authority in the land. As for refuting them and exposing their falsehood and warning against their rhetoric, then this is an obligation on all those who have knowledge and ability.