Suppose someone has walked up to the Continental mechanic and told him that if he installed the wear strip incorrectly it might fall off. And just maybe it would fall off on a runway. And maybe the next airplane to take off would hit it. And maybe that next airplane would be one of a handful in the world that, as it would turn out, could suffer a fatal crash if a tire hit the metal strip. And if that happened, 10 years later he might be sentenced to a suspended jail term in a country he may never have visited. My guess he would have said "yeah, right" and gone on with the repair. And even if he had changed his ways, I think it would have been for fear of causing a crash, not of getting a suspended jail term.
Of course, it's important to deter unsafe practices, but it seems to me that a punishment that's less likely than winning the lottery isn't much of a deterrent. Supervise the mechanics better. Make the airlines accountable for ensuring that their airplanes arrive with all the bits of metal they left with. Do a forensic examination of every piece of FOD that ends up on a runway. I don't know if any of those are feasible, but they'd all be better deterrents than what happened here.
I'm not saying the French law or French court was right or wrong. Laws can serve as deterrents, but that's not the only reason they are passed. And presumably the French legal system wasn't established as an aviation safety system. But I think it's hard to justify the verdict on the grounds that it will improve aviation safety.