Is it so unreasonable to have one spare bedroom?
Home owners can be a bit self-righteous about the fact that they've had to pay for their home, etc., etc. We had to pay for our home, and it's a long slog, but at least at the end of it we've got an asset that we can sell and utilise the money to downsize and maybe help our children. People who have been unable to buy a home, have no such asset, and now have no security either.
I have every sympathy for private renters who may live in cramped accommodation. It's a horrible situation, but I don't think turning on other people in a slightly better situation is going to solve the problem.
I can see that it would be reasonable to encourage, for instance, a single older person to move into smaller accommodation. But, as others have said, there isn't necessarily smaller accommodation available.
This whole thing seems like a complete shambles.