Just tell your broker to not loan your shares. If they weren’t bought on margin then they won’t loan them out. Standard broker agreements for margin accounts state that your shares can and will be lent. Sometimes you’ll even share in the profit from loaning them as in-demand assets for shorting often have a borrowing fee.

The analogies hold though - people sell things they don’t own all the time. The important thing to understand is it is based on promises to deliver an asset/money by a certain date.

Likewise people buy assets on margin all the time. This means people can buy things they don’t have money for based on a promise they will pay that money back. Credit cards, mortgages, auto loans, bonds, etc.

This is how our finance system works and for whatever problems it has, the future promise concept isn’t one. Especially with the regulations and limits on it.