Buying 'smart' TVs also sends a signal to the manufacturers that this is what people want (as some here have suggested). It perpetuates the delusion that ad-ridden TVs are acceptable. Vote with your wallet and buy something else.
It's also somewhat profligate to buy hardware and deliberately disable it (although I entirely understand the motivation and hacker ethos). That hardware represents sunk resources. Buying it to ignore it leaves a bad taste for me. Electronics manufacturers are ecological bad news, in general. I'd rather not contribute to unnecessary manufacturing if I can avoid it.
Regarding quality of image, I kinda suspect that the necessity for ultra-high def TV has been over-sold. Sure, for gaming, home cinema, etc it might be a real concern for some. For me, I've got a genuinely dumb TV and nobody has ever commented on the image quality for TV or movies or gaming (Switch). But maybe this is one area where the visual equivalent of audiophiles will never be dissuaded :)