calendar that isn't booked is just free for the taking by any random person.

Isn't it nice to have plausible deniability when someone wants to book you, but your default work activity (i.e. blank on the calendar) is more important than their meeting? Aren't there some things where for your boss or key customer, you are free to meet, but for some secondary priority you are busy?

I guess your use case is really that you have people that you agree you need to meet with, so finding a time really is just a matter of them finding an open slot and not so much a question of placing them precisely in the pecking order of potential activities (e.g. is this meeting more valuable than my slight preference for morning flow, etc.). The issue of people feeling entitled to your time (whether this is a problem or not) doesn't change either way, even if you insist on writing 3 emails for every meeting you schedule.