It's a union's job to advance its members' best interests, and (arguably) keeping physical schools closed was just that.
I don't agree, but I understand why they did it and why they'd push that agenda with the CDC.
It's when the teachers' unions start saying "it's about the children" when it's actually about their members that they lose respect. Again, not that they shouldn't be aggressively pursuing their members' best interests - just leave "the children" out of it.
When 1,200 public health officials opine that protesting state lockdown orders is wrong but demonstrating against institutional racism is right and must be permitted even if it spreads COVID-19, then that costs them a lot of respect.
When teachers say they need raises or to keep schools closed "for the children" but then continually back their worst performing members, then that costs them a lot of respect.
Public health officials- not all but a significant minority - and the teachers' unions "spent" a lot of their accumulated respect over the past two plus years.