1) Besides access control, having an unencrypted WiFi network is not great because your entire internet/local traffic is open to be sniffed. High-gain antennae, etc. You are essentially screaming the contents of (what would be) your ethernet cable into the void.
2) Access control is exactly the point. I suppose you could ban the TV's MAC address from your open network (and I suppose a sufficiently malicious TV firmware could randomize its MAC address), but your stated purpose (allowing open network access) is not exactly compatible with what you presumably wish to do (disallow network access to a smart TV).
Wifi encryption is the wrong layer anyway. Point to point tls is what you want to depend on. and sometimes I dream of the never realized ad-hoc ipsec connection, the actual correct layer to do encryption on. but ipsec was killed by it's own incompatible complexity, so tls is a good second best.
I run an open access point and depend on tls or ssh to protect my traffic.
2) Access control is exactly the point. I suppose you could ban the TV's MAC address from your open network (and I suppose a sufficiently malicious TV firmware could randomize its MAC address), but your stated purpose (allowing open network access) is not exactly compatible with what you presumably wish to do (disallow network access to a smart TV).