To play devil's advocate (and let me be explicit: I think this would be a horrible idea) the benefit would be cheaper flights, which would in turn have benefits such as cheaper shipping costs (for air delivery), more people experiencing other cultures (which I believe, perhaps naively, would be a social good of its own), promote remote working (since it's now easier to fly people in for meetups etc), and boost tourism economies.

Increased/cheaper travel would also come with some bad externalities: Increased CO2 emissions, and possibly increased rates of cancer (high altitude is a high-radiation environment - not enough for the occasional flyer to worry about but it can add up). ...and of course the externality that lower safety controls means occasionally one of these more frequent flights will fall out of the sky.

One way to think about these kinds of questions is to reverse it - suppose flying had 10x stricter safety controls than it does today. Would the world be a better place as a result? What would be the downsides?

EDIT: I almost forgot perhaps the most important one: If flying is more convenient/cheaper, even if it's slightly less safe than currently, it is still FAR safer than driving and a shift from people driving to people flying means that relaxing flight safety may actually SAVE lives.