That would be a very bad product design decision. I would realize that I had made a bad purchase and I would return the TV to the store and buy one that didn't do that. There are lots and lots of TVs to choose from. On the other hand, if you really like AppleTV, you might not care. Either way, it is the consumer's choice, so no harm. Lots of TVs have features people don't like.
>There is a case to be made that such anti-competitive behavior is illegal.
No there isn't. iOS is a minority platform (globally) by a very large number. Also, there are a number of app based messaging options, many of which are quite popular and some use strong encryption.