Actually think though the things you're saying when you say them. People generally don't put thead elements in tables that are used for positioning. Even ignoring that, there is no definition of "break" besides the most contrived and tautological for which allowing people to see table headings would break anything. Bolstering low-effort concern-trolling as if it's high-value commentary (i.e. well-received middlebrow dismissals) is known to be a problem on HN, and you're not making it better.
No it wouldn't.
...it absolutely would, yes. Tables are used everywhere, including for positioning stuff.
Actually think though the things you're saying when you say them. People generally don't put thead elements in tables that are used for positioning. Even ignoring that, there is no definition of "break" besides the most contrived and tautological for which allowing people to see table headings would break anything. Bolstering low-effort concern-trolling as if it's high-value commentary (i.e. well-received middlebrow dismissals) is known to be a problem on HN, and you're not making it better.