Tolerance? of others' sins? Are you serious?
Celebration of immorality is merely the celebration that they won't be alone in their sin. They want company.
It's all about pride and selfishness.
Tolerance for sin and sinfulness is more often the consequence of an overly selfless person than of a selfish person.
To be righteous, one must be righteously selfish. Humble, selfless in some measures; at the root of the soul — selfish. One has to hold onto one’s good soul for all get out, and not become wholly subsumed into the “blob”, the mob, the group.
It is like a siren call to join the group, to be subsumed into a group identity. That is also a form of selflessness.
And there are groups one should be such a part of, selflessly. But these are not easy to be part of, nor should they be.
Arrogance is probably a better source than pride and selfishness, as pride and selfishness are simply variations of arrogance.