> It's not more cruel than introverts forcing extroverts into not socializing.

Well that's the point: Society has made it acceptible for extroverts to force introverts into socialising, but the other way round is somehow inacceptible.

> Having fun at work is no more a right than not having fun at work is a right.

Having or not having fun is no right in itself anyway. Companies that force introverts into situations they are uncomfortable with are eventually going to lose them. The extrovert's fun stops where it is actively harming the introverts. Undermining introverts' feelings by making them feel uncomfortable in order to have fun is harassment.