I wouldn't ask my parent/grand parent to isolate, if they don't want it.

>And 1 in 20 people over 70 obviously isn't low

People in over 70 has already high chance of death regardless of covid or not. So given that they are infected with covid, 1 in 20 chance is not high.

That this is not some uncontrollable inevitability is the whole point. Places that were proactive have less economic harm and far less death and illness. I suppose people aren't going to change, so the ship has sailed for much of the world, but it wasn't inevitable for vast numbers of people to get infected.

As far as 1/200 being subjectively low, if something had a 1/200 chance in killing you, would you do it 5 times a day? We can answer probably not of course, because you probably wouldn't do it once a week (or you wouldn't be).

If I'm in this age group, obviously I would happily take this chance, if the alternative is lockdown/restriction.

It would probably be considerably more fun to self isolate while taking up drinking, smoking, motor biking without a helmet and a variety of other risky activities. At least those are interesting, and they are probably less risky.