Some runners love treadmills, some hate them. I’m more in the latter camp, although I definitely appreciate them at times. I have one in my garage, and just knowing it’s there is a source of comfort. Blizzard coming tomorrow? Not my first choice of offerings from the weather gods, but I know I’ll still get a run in, either outside if things aren’t totally ridiculous, or on the treadmill if I decide that overall my experience will be better by staying inside.
If running on a treadmill is going to mean you run on days that you otherwise wouldn’t, then have at it. I’ve certainly had winter runs where afterward I grudgingly acknowledge I’ve chosen incorrectly and would have had a more positive experience by hitting the treadmill. There’s no denying the safety factor of the treadmill in bad weather winter, especially if you would otherwise be running in the dark with uncertain footing.