I have a friend who owns a construction company (a civil engineer) and we talked about this whole heating home thing a while ago when we were in a bigger group. There was one woman who is extremely "eco" and said that she never turns on the heating unless it's really sub-zero outside.
The engineer friend said that in Germany and similar climates, it's a surefire way to destroy your home and is not eco-friendly. As many have said above, the humidity will cause condensation, leading to mold. In the longer run, you will likely need a major reconstruction of walls or of the roof and may need new pipes. All of that, aside from being expensive, would have major eco-impact, as the materials used are designed to last much, much longer when cared for properly. He said that 20-21 degrees Celsius isn't only the range where most people feel at comfort, it's also the least likely to cause issues in the long run /has the best long-term financial payoff when you consider the cost of heating itself.
Telling people to "heat the person, not the home" is tone-deaf to those who struggle to heat their homes in general. Of course, some people need to be told that they could just throw on a jumper and don't waste gas on heating a home, just because they like to be toasty year-round. The people struggling to heat their homes are probably bundled up to their noses already, I'm sure they won't need to hear that (most of them, at least). Same as boiling only the water you need. I don't think many people boil 10 litres of water to throw 9 down the drain again.