Things like commercial flight and the space program show that reasonable levels of caution can be routinely applied when lives are at stake.

The usual situation with engineering is that you can have whatever level of safety you are prepared to pay for.

As I understand it, most lives are currently lost to engineering through society-approved tradeoffs - in the form of motor vehicle accidents. We know how to decrease the death rate there, but getting from A to B rapidly is widely judged to be more important.

It is easy to imagine how machine intelligence is likely to produce similar effects - via unemployment. We could rectify such effects via a welfare state, but it isn't clear how popular that willl be. We can - pretty easily - see this one coming. If the concern is with human lives, we can see now that we will need to make sure that unemployed humans have a robust safety net - and that's a relatively straightforwards political issue.