It's funny how this (imo) almost feels like an inherently inert topic to discuss:

Is it dumb of them to do this? Not really, they got unlucky with the timing and they already designed the machines. Selling them below cost to subsidize steam-sales would probably create bad incentives for them.

What will this mean for Valve's future? Nothing, they're still a relatively lean company with a money machine.

Will this dissuade them from creating hardware in the future? Probably not, the Steamdeck was really succesfull and they've got more than enough resources to do a few failed experiments.