I agree this is entirely unprofessional, however teachers now seem to have the status the police used to 30-40 years ago, where they can behave as they please, are not held to account and you're not allowed to criticise them.
What's clear is that most teachers (and I include this head, and the unions) don't have any concept of risk or any grasp of the reasons for lockdown (to protect the NHS and slow the spread, which we have done) nor the fact this isn't going to go away anytime soon, or even at all.
Earlier this week I found myself engaged in discussion with a teacher who believed that it would be safe to go back by September, because the virus 'would have died out by then'. Now this isn't exclusively a teacher problem, half the population don't understand the reason for lockdown or the risks, and are bleaching their shopping etc, but it's worrying because teachers are responsible for educating our children.
And they have influence - some parents, especially if not particularly well educated, will defer to a teacher's view. So if head says 'its not safe for us to be at work' then those parents may well a) agree and b) be scared out of returning to work themselves.
If teachers get their way on this, schools go back in September or later. But the later this date is, the more risk there is that the next peak is in winter and the chance of the NHS becoming overwhelmed becomes more likely.
The real risk is very low to any healthy person. Some people will die, but people die every day anyway. Everything we do involves a similar amount of risk, a number of deaths occur every year from falling downstairs, yet we do that every day. No one's telling us all to move to bungalows!