If we go with 'let it rip, it's just a cold', (and people are pressured to come in and work whether ill or not) this is known to be highly contagious.
So from your infected staff, a high proportion of your customers will probably get it.
They'll pass it on to whoever they come in contact with.
And as people keep pointing out: a percentage of people who catch this will need hospital beds, and it will be serious. If a large percentage of the population are currently ill, then the percentage of those in hospital will be more than the NHS can cope with. Not to mention the hospitals, fire services, police etc having a lot of people off sick who haven't got the mild end version. The people who will die will not just be the few with extreme end covid, but the people having heart attacks, strokes, car accidents, births going wrong, people stuck for days in casualty. People who needn't have died had we not had the entire country off sick at the same time.
Why isn't hospitality closed? Because the govt haven't got the money or nerve for another lockdown and are hoping that the minimal stuff in place like the isolating stops it going so mad there's a serious problem. It's Johnson's MO. Wait and wait until he's absolutely sure all hell has broken loose so it takes 3-4 months to pick up the pieces again.
There aren't any easy answers, and it's shit. We get this.