I don't buy that as an argument. It's the same argument used to push all kind of hoaxes or fad stuff. We live longer than what we used to do, so not everything we did in the stone ages can have been beneficial.
Average lifespan has increased, meaning more people survive early deaths due to disease and injury that we can now prevent, but as individuals we haven't broken through any maximum age barriers.
That said, sun bathing is a modern phenomenon. Our ancestors knew enough to assess that painful sunburns were bad and mitigated their exposure by wearing large hats and clothing with long sleeves. I'm sure even primitive peoples would cover themselves when necessary. If you spend a lot of time working outside you also develop a very dark tan which helps quite a bit. Modern people seem to suffer mostly from spending so much time indoors that even moderate sun exposure on the weekend produces a damaging sunburn.
