Except you usually have a very dry environment when heating due to the lack of moisture in the colder environmental air, and need to add moisture to avoid falling out of healthy humidity levels for human beings.
We are talking about large amounts of moisture that need to be added to the air when heating. There is 0 risk of mold in that situation. Ideal humidity: General recommended range: 40-60%; ideal/goldilocks humidity, 50%; mold conducive conditions: 60%+; air when heating: often ~30%.
Perhaps if the house leaks air like a sieve and you just compensate by more heating watts (or if you use some fancy heat recovery ventilation), but in a properly closed shell, with considerable cold outside, your primary problem is getting rid of all the humidity human life produces without the water condensing on whatever surface is coldest. I suspect that we are talking about very different environments.
If you have a house that tight, you need to compensate by a certain number of minimum forced air changes per hour, on top proper ventilation in your bathrooms and kitchen. In fact, modern building code in the US, and likely throughout most developed countries, requires a tighter envelope than the minimum number of air changes per hour, thus requiring, intrinsically, that all houses have ERVs or HRVs. This is all a solved problem, and you are never going to need to dehumidify during the heating season if you are respecting the principles of building science. It is possible to build "too tight" by neglecting basic ventilation principles, but that is not what I would call "properly closed".
Properly built modern houses would certainly not be the realm of slightly less bad resistive heating improvisations. But here in Germany we have plenty of old stock modernised to the point where is sufficiently air tight for insufficient ventilation to become an issue (and often it does!), but not to the point of active ventilation. Moisture buildup is a major concern, particularly at times of heating scarcity (which is when improvisations become more likely) As I said, different environments.
