I think stem shifters are more likely to shift out of the way than impale you. You'd have to impact the lever exactly vertically or on an off-vertical vector that pushes the stem against its stop for the lever not to want to shift instead of impale, I'd imagine.

In reality normal riding-down-the-road type riding results in crotch-to-stem accidents so infrequently, it's of next to no consequence what type of shifters you've got.

Heck, even most BMXers stopped running stem pads years ago.

If you stay in your little ring and smaller cogs, stem shifters can actually widen the impact zone and soften the blow of the stem: