A common teacher complaint, IME, is an expectation that they should be ready and willing to sacrifice anything because of their love of the students. Teachers have every right to have their own interests represented.
Much as I'd like to see our schools re-open, I wouldn't sign up to be the school nurse for anything. Every single kid with every slight Covid symptom is going to come to my office with their poorly fitting badly worn masks. What a nightmare.
Using data on the reopening decisions of 835 public school districts in the United States, we find that school districts in locations with stronger teachers’ unions are less likely to reopen in person even after we control semi-parametrically for differences in local demographic characteristics. These results are robust to four measures of union strength, various potential confounding characteristics, and a further disaggregation to the county level. We also do not find evidence to suggest that measures of COVID-19 risk are correlated with school reopening decisions.
If unions were really the fundamental problem it would be hard to explain why those other educational systems can be so much better than the USA's.