Tolerance

In plain terms

Tolerance is not approval. If you approve of something there is nothing to tolerate.

The concept requires three things together: you object to something, you have the power to stop it, and you deliberately do not. Remove any one and it is not tolerance - indifference is not tolerance, and neither is powerlessness.

Which makes it a stranger virtue than it looks, because it asks you to permit what you believe to be wrong. The reasons offered are that coercing belief does not work, that the power to suppress will eventually be held by your opponents, and that a society of people who disagree needs terms on which to continue.

And it has a limit that will not go away: whether a tolerant society must tolerate those working to end toleration.

As a philosopher would put it

Locke's argument is partly epistemic and partly about the nature of belief: the magistrate has no more reliable access to religious truth than anyone else, and coercion produces outward conformity rather than the inward assent that salvation requires. Mill's is developmental - truth needs contestation, and even false opinion sharpens the grasp of true ones.

Popper's paradox of tolerance is the standing problem. Unlimited tolerance leads to the disappearance of tolerance, since the intolerant will use the liberty they are granted to destroy it; he concludes that a tolerant society must reserve the right to suppress intolerance, though he preferred argument and treated suppression as a last resort.

Marcuse's repressive tolerance runs the other way: formal even-handedness in conditions of unequal power favours the established position, so tolerance can function as a mechanism of the domination it appears to soften. Forst's contemporary account distinguishes a permission conception, granted by the powerful, from a respect conception between equals.

What is actually disputed

Where tolerance ends.

Popper's answer is that intolerance may be suppressed when it refuses argument and answers with violence, which sounds workable and leaves the hard cases unresolved: the movement that is currently peaceful and openly aims at ending pluralism.

The liberal instinct is to tolerate anything short of incitement, on the ground that the power to suppress will be inherited by someone else. The militant-democracy answer is that this is exactly what failed in the 1930s.

Marcuse's objection is different and unanswered by either. If tolerance is extended equally in a society where the parties are unequal in power, its practical effect is to protect the arrangement that already exists - so a genuinely even-handed policy is not neutral in its results. Whether the remedy is worse than the disease is where the argument has stood since 1965.