Exactly what you said. Even if I do my very best to secure my router and blacklist the TV's Mac address (and never give it the wifi password), how do I know that my neighbours won't mistakenly let their WiFi open for a day or two until they realize their mistake? Or if I tether my mobile data from my phone and turn into a router, that I might forget to secure it?

All it takes is one small slip.

I'd rather never take the risk. I'll just look for a dumb huge TV; I need 65+ inches, good luck to me, right?