[gnaffle]

I'm pretty sure that as UAVs increase in capabilities and come down in price, there will be regulations that force them to carry alerting / avoidance systems (like FLARM or similar) and light aircraft will have to carry them, too.

Just like in many countries, restrictions on the sale of high power laser pointers are in effect and vastly limit the amount of people that have easy access to them, and therefore the risk of someone doing something stupid.