It is avoidable, but not daft.
I work in a large secondary school and the mitigations imposed by the government are utterly inefficient. Especially with the new variant.
We've had 3 cases on Monday morning, and out of those 3 cases, another 6 self-isolating kids have now developed it. So in theory, the 'chain' has now been stopped. If those kids were not sent home this morning, we would be up to 18 cases by the end of the week.
Another case appeared this morning, but it's in a different year group.
The main issue here is that our school has imposed the wearing of face masks in class (despite government guidance) but many parents are discouraging their kids to wear them and ask for exemptions because of 'mental health'.
We open the windows and doors. That's it. no other ventilation or air filtration system can be installed as the school has no budget (we've had to make staff redundant and those leaving are not replaced unless absolutely necessary).
My guess is that if we don't ask kids to self isolate, we would have 100+ cases within two weeks. And those kids are likely to give it to siblings who will pass it around other schools.
I'd prefer to have 60 kids self isolating and well, rather than 100+ kids sick at home transmitting the virus to other people in the community.