A US political commentator (Kyle Kulinski, IIRC) used a pretty decent analogy on this point some years ago. I've probably modified it.

If a driver runs down a pedestrian and claims it was an accident, he might end up with a manslaughter charge or some judgement far less harsh than "vehicular homicide." If that same person runs down a pedestrian every fucking time he takes the car out, the "it was just an accident" claim is at some point going to be unbelievable, and it is clear that the dude goes out killing people with his car.

Ukraine, Yeman, Somalia, Syria, Libya, Iraq, Afghanistan, Yugoslavia, are all countries we said we were going to save in the last 25 years (there are more) either directly or working with / through others. Every one of those countries was at least partially destroyed, and NEVER did the claimed "peace and democracy" result from our invasion/bombing/intervention. Not once. We ran someone over every fucking time we took the car out of the garage.

I know that analogies are not a good method to convince someone to change their mind, but I think that is a pretty good one.