I absolutely do get that schools school be made as safe as possible for teachers, but we can't delay going back the impact of not returning or returning very part time will be huge for education, the economy and vulnerable children.
What should be happening is looking at ways to make it safer, more handwashing facilities, sinks and taps should be being installed at entraces/exits now (as private nurseries and forest schools have done). Pupil movement in secondaries restricted where possible (teachers moving instead of pupils for non practical classes) , other spaces such as leisure centres and games halls used for teaching so that distancing can be managed. Furloghed Council staff brought in to assist in increased cleaning routines. There are lots of ways to manage the risk but get everyone back.
Track and trace seems to be working so far, so we can now manage local outbreaks better.
I don't think teachers are dispensable but we do need to get schools back. Lots of other workplaces are now returning where staff have also have contact with thousands of people per day in small, non ventilated spaces (shops, restaurants etc). OK they are wearing masks but people are touching them and wearing them incorrectly making them ineffective against the virus anyway.
My dp has worked throughout the pandemic in a busy NHS department, in close quarters with lots of other staff, dealing with equipment some of it has been used on covid patients (think factory production line kind of work ). They don't wear masks, it's not part of their PPE requirement, but they do wear plastic aprons and rubber gloves. Not one member of his very large department has caught covid despite being in close daily contact.
Dentists, nurses, physiotherapists, hairdressers, early years staff are all back to work. I don't see how teachers are all that different, we can take measures to minimise the risks.