Yeh, thanks, obviously I know that now.
When I said I accidentally booked the second reservation, I don't mean the second reservation was the accident (duh). I mean it was accidental that I didn't cancel the first one before booking the second one.
I am also a host who offers free cancellation. I have had many people cancel on me. When it's done promptly, it's no inconvenience whatsoever.
"It’s not natural. Rather, it’s bad form to tie up a host’s calendar when you have no intention of staying."
I fully expect that when I offer free cancellation, people will book my place as a safety option, then cancel if they find something better. It's not bad form. It's normal consumer behaviour. It's also something that's allowed on other booking websites.
It would be so so easy for Airbnb to introduce a warning system when someone is about to book a second reservation with overlapping dates. But they don't. Instead they just let people fall into the trap that's laid for them.
No one is going to read beyond "free cancellation before [month, day]".