Backlash? As in the UN sending them a letter saying they "the bad country are being bad boys" because they didn't follow rules?

Though its debatable whether it breaks the rules or not, gauntanamo is the most obvious example, if we assume it isn't against the rules imagine the even bigger pr backlash for something that is against the rules...

Unless, of course, you lose.

Well that isn't really applicable to any developed countries at the moment, they don't do unwinnable wars (well unwinnable against enemies military, occupation is a whole other problem)

I would be more supportive of rule breaking if the fight is literally life or death for our country, only if the enemy is using some tactic that is amazingly effective and against the rules that is winning them the fight, outside of that narrow definition we have no need to break the rules and it costs us very little to follow them...

IMO it gives us more benefit by following them than it costs us to ignore them...