The environmental benefits are massive. For all the press the climate gets you'd think we'd hear this angle more. Perhaps even incentives for employers.
This is very place-dependent. In california where everybody is driving to work, you're probably right. But in many European cities where people would take public transport to work, and instead are heating entire homes all day instead of heating one office for hundreds of staff, the environmental effect of WFH is probably negative.
Ditto this. This summer I'm going to need to run my air conditioning basically 24/7.