Personally, I like that UTC is the default time zone. Processing of dates should happen in a standardized time zone. It’s only when you want to display it that the date should become local.

UTC is a fine default time zone, but that doesn't matter here.

A datetime with a timezone and a datetime without one are two different things, both of them useful. My birthday does not have a time zone. My deadline does.

The company deadline for getting some document returned? It might or might not, that's policy.

Poetically: we are born free of time zones. We die bound to one.

This will result in incorrect behavior when, between converting to UTC and back to the original timezone, the timezone database has changed, which happens more often than you think.