can't you buy 4K UHD blu-rays?
That said, it’s not great for the environment, probably still worse even when comparing with the ecological footprint of data centre infrastructure (download-and-keep would be even better than streaming actually). Not everything gets a (timely) release either.
Sometimes a quick download would be great. FWIW I’m on a 400mbit/s connection.
Obviously DRM free versions would be the cherry on top and would guarantee “portability” into the future (I’d still buy the n-th version of The Terminator in 8K in any case ;)
If I'm going into criminal land either way I'm just going to pirate in the first place.