Bruce posted one of the major scientific reasons for opening now - the 'immunity debt'.
COVID-19, influenza, and the respiratory virus Respiratory Syncytial Virus (RSV), could push the NHS to breaking point this winter, a new report says.
www.imperial.ac.uk
There's a strong argument for opening now, alleviating some of this 'debt' during the summer/autumn months, so as to lessen the pressure in the winter.
If we kept 'locked down' to any degree, all that happens is that debt gets worse. It's what Johnson meant when he said "if we don't open up now, when do we open up", because you can't end lockdown in the winter as COVID will have an 'exit wave' around then regardless, meaning we'd be locked down until at least the Spring, and we don't know what the scenario would be then regardless.
Personally, I think they've timed this extremely well. Bizarrely, as they've screwed so much else up. Yes, we'll have hospitalisations and deaths now, but to nowhere near the degree of previous waves and it'll mean we're in a much better position from November onwards to deal with the overall situation.