That's a bit of a misconception, TV's have other potential paths to try and get themselves connected. Say connecting itself to an unsecured network or uploading through a data stream over HDMI. Or you sell the TV and the next person connects it to the internet (TV's can store a lot of data too).

The only real ways to cripple a Smart TV is to either destroy the ability to spy (disconnect mics etc.) or properly contain it in a firewall.