"Perhaps the sentiments contained in the following pages, are not YET sufficiently fashionable to procure them general favour; a long habit of not thinking a thing WRONG, gives it a superficial appearance of being RIGHT, and raises at first a formidable outcry in defense of custom. But the tumult soon subsides. Time makes more converts than reason."
What does he mean in this statement? What twentieth century examples support this observation?
What he's saying here is that people's attitudes towards things change. They change their minds on what is right and wrong. Sometimes they hold on to ideas and values just because they are customary.
You can point to such things as not allowing gays to marry, or not allowing women to serve in combat units in the military, even when combat no longer requires physical strength.
On the positive side, you can point to things like the ending of most racial discrimination. This is, at least possibly, because of the passage of time, not because of reasoning.