Hans Oberdiek, in his (swell) book Tolerance, has argued in support of tolerance as a virtue, on substantively liberal grounds. In addressing some worries at the end of the book, Oberdiek accepts that it would be a mistake, in his view, to think that liberalism (of his variety) is fully neutral, and that a defender of liberalism--and along with it, the value of tolerance--should admit this. I'm not as interested in his response to these worries as in an assumption that seems implicit in his overall discussion: that tolerance itself is a distinctively liberal value (derived from the value of personal autonomy).
Tolerance is an attitude of forbearance and restraint toward others. It is conceptually distinct from the act of toleration, which, I think, is possible to do "intolerantly"--that is, I might tolerate something because I value peace more than aggression, while still judging that the activity or practice to be, in itself, intolerable. This may seem paradoxical, but I'll leave the paradox for another time. Presumably, the view that tolerance is a distinctively liberal value stems from the idea that its value comes from the way it promotes individual autonomy.
I think, however, there's a way to derive the value of tolerance from values that aren't exclusively liberal (e.g. in the sense of invoking personal autonomy). At least, they are values to which liberalism doesn't, I think, make a distinctive claim. (Maybe I'm wrong about this or misunderstand liberalism.) I'm thinking of two basic values: respect for humanity (as for example in Kantian thinking) and humility.
Now it is true that Kant prizes autonomy, but respect for humanity extends to persons who are not themselves autonomous (e.g. infants and those with severe mental disabilities). That we should respect all of humanity means that we may never treat others as mere means, but always as ends in themselves. Call this the recognition of the humanity of others (and ourselves). In itself, I don't see that this is a distinctively liberal value.
Humility has to do with our attitude toward ourselves. It involves recognizing our own limitations, frailties, and the possibility of making errors (for example, in judgment). Humility thus involves, in a different sense, the recognition of our own humanity: the recognition that we are, after all, only human--not angels or gods.
It seems to me that the value of tolerance toward persons can be derived from these two recognitions. If I am, after all, only human, then I have to recognize my own limitations; at the same time, since others are persons, too, and worthy of basic respect, humility seems to demand that I extend not only respect, but also tolerance of them as "only" human, and thus liable to (what I think are) errors in judgment and action. Where deep moral disagreements emerge, this might, for example, entail that I should try to restrain my tendency toward intolerance (and intoleration) of others where the disagreement seems fairly substantive and where I cannot (reasonably) simply dismiss these others as "mad" (say, like Ted Bundy was). I should respond to these people, as persons, in a spirit of tolerance, even if my own judgment leads me to hold that some practice or activity of theirs is, in itself, intolerable.
In a prior post, in "defending intolerance," I was thinking primarily of beliefs and actions (or practices) as objects of tolerance and intolerance. Putting this together seems to lead to a "tolerate the person, not the practice" sort of idea, which seems (to me) rather uncomfortable. That is, people are often so bound up with particular commitments and practices that these things are constitutive of their identities as the particular sorts of persons they are. I've always found the "love the sinner, hate the sin" view not entirely convincing for this reason. So there's a lot of work left to do here.
(One possibility is that if we start with persons, the value of tolerating persons may lead us down a complicated road of understanding the place of particular practices in their lives which we are inclined to judge as morally unacceptable... OTOH, a "liberal complaint" might be that this variety of tolerance is going to be too weak to pull much weight. I'll have to think more about that...)