This isn't just about schools. It's about the infection rate in the community.
Everybody accepts that there will always be a risk, but it would be downright stupid and irresponsible not to be aware of the high risks - it doesn't take much to realise that and to realise that there is no solution without extra resources. A positive attitude coupled with a laid back "let's see how it goes" approach just won't do.
Even if distancing rules are relaxed to one metre, it will still be impossible (no matter how positive people are) to maintain that distance with 30 children in a class. One way or other, twice the space is needed. An estimated 250,000 additional adults are also needed, in addition to extra hand washing and toilet facilities, etc.
At the moment, the average percentage of people showing symptoms is 0.5% (with many variations across the country). Some people, especially children. are apparently asymptomatic. That means that, on average, in a 2000 pupils secondary school, at least ten are infected at any one time.
Secondary school teachers usually take five different groups of pupils a day, so the chances are high that they will come across an infected pupil. The pupils themselves usually move between different groups, so consistent "bubbles" can't be maintained.
If all pupils return in September and the rate of infection stays as it is, it will only be a few days before nearly the whole school is infected, just as happened in care homes. Some of the staff will have underlying health conditions. Some of the pupils will take infection back to their families. It is unrealistic to think that some people wouldn't die.
The only solution is to get the infection rate in the community right down - maybe to 0.1% and to have a super-efficient test and trace system, so that any infection can be identified quickly (within hours) and small groups are isolated.