The difference between Cummings flouting the rules and people flouting rules on a beach is that, presumably, the people on a beach don't know whether they have Covid 19.
Both Cummings and his partner had tested positive or at least had symptoms. I can understand (from a parental point of view) why they decided to travel. If your parents have a property or annexe where you can isolate but are close by to take your child if you both end up in hospital it seems a solution. You may well take a chance, if the grandparents were willing, to ensure the safety of your child.
My dread, as it is with many parents, is that the adults get hit badly at the same time with the virus and the children are left to fend for themselves. Even on a basic level someone has to make the decision to call an ambulance - which a four year old can't. And this virus can change very, very quickly. So I can understand the thought process, though I'm not supporting it.
But, Cummings had more knowledge than we, mere mortals, about the virus at the time. It's not the moving in to his parents that's the real issue here. Some families did move in with grandparents - especially if there was dementia to deal with or having the kids looked after by gran/grandad meant the adults could work.
The thing with Cummings is that he took the decision to travel KNOWING he was ill, as was his partner. They were contagious. You're not telling me they didn't stop at all. OK, with petrol you could do a 'self service pay by credit card' type pump and use gloves. But I don't know any way of isolating yourself on a motorway if you need the loo. And with a four year old in the car on a 4 -5 hour plus journey you're likely to stop more often than just adults.
So he has, potentially, knowingly infected umpteen people on the motorways between London and Durham. Most of whom would have been key workers as no-one else was supposed to be travelling at the time.
That's rather different to people sitting on a beach assuming they don't have the virus and behaving like prats.