Of course anti theft serves the manufacturer. And I think that is ok. If you have a stolen product, you have 0 rights to use or posses that product.
Once you purchase the product legitimately, you now have legal protection so that the OEM may not lock you out. Products should respect the owner. Stolen products are still owned by the OEM and not the person physically holding the product.
Almost appropriate. 99.99% of houses are never robbed and yet everybody locks them. Of course we can leave our doors unlocked and that's the difference: choice. We should be able to turn off DRM. I can accept that without DRM I can't watch that streaming service (even if there are many ways to circumvent and/or to prove a purchase) but not to use a product for my own sake (eg: run my software on it.)
Without going to entirely FOSS TV firmware, I'm not sure how this matters at all. It will never trigger for legitimate buyers and if it ever does somehow, you call the company. If they do not cooperate, you take it up with your consumer protection agency and they fine the company for you.
But the reality is that it never will activate and you wont ever know about it so it can't possibly impact your life and there are appropriate safe guards against misuse. It's about as useful as asking why you are forced to use a specific brand of flash chip on the image processing board.
Once you purchase the product legitimately, you now have legal protection so that the OEM may not lock you out. Products should respect the owner. Stolen products are still owned by the OEM and not the person physically holding the product.