I always have all my seat belts fastened in their buckles, both in the back seat and the passenger seat. But I use my driver seat belt as intended, as I consider it a life saver. It's an automatic gesture to fasten it when I get behind the wheel. I don't even remember that I fastened the seat belt. But if I forget, I immediately have the uncomfortable feeling that I missed something.
The passengers in my car are completely free to use the belts or not. However, if they don't use them, they have to walk.
It's that simple.