Because you get into a car and drive on the road, knowing full-well that car crashes happen, you are then making a choice based on risk-assessment. Unfortunately, many people don't think a bad car accident will happen to them (or many don't think about it atleast in the day-to-day), they get in the car expecting to get from A to B, but the act of driving is where our ability to judge the risks really counts. Being aware of and following the guidelines for road safety is paramount, we cannot always determine what other road users will do - but we can take precautions to make sure we are protecting ourselves as best we can (safe driving/seatbelts etc). That's called personal accountability. in the event that we have a crash that is someone else's fault, then that is something outside of our control, but the analogy can hardly be used in parallel to abortion, because the innocent party had no say in whether it lives or dies.
The Christians (and the lions) are still the innocent party in that scenario^ but the choice to believe in something and the choice to act on those beliefs (especially if it's violent) are 2 completely separate things. So again, not in any way parallel to abortion.