Maybe it's on a sliding scale but one that is not linear, we know when the curve goes exponential and I suspect they do too.
Single digits and killed in an indirect fire incident will probably not get Kharg Island or Tehran turned to rubble but it will get something destroyed of value with the intention of killing Iranians in the process, both sides know that this is a function not equation.
As to consensus, yes required for major, on going actions; responding in kind or some multiple of it to punish, dissuade, preserve honor and reestablish deterrence, no. Congress is necessary in the overall scheme of things but not where the direct action needs to happen. The pax on the jet can tell the pilot about the ride but ultimately the pilot is in control, duly noted. Now when the jet the lands the pax don't have to buy another ticket and without that the jet doesn't go, they have an input just not at every moment.
LOAC does not prevent destroying civilian infrastructure if said infrastructure is used in war making / supporting activities, for the attacker it is a matter of how many degrees of separation from said war making activities you believe are required before you consider it off limits.
Mosques used to shield fighters are legitimate targets, hospitals with AAA guns on them are legitimate targets. POL facilities that support directly or indirectly war efforts of an enemy (state or non-state) are legitimate targets if you trace the economic output of them to the enemy inside of the range of separation you deem appropriate for military action.
Will respectfully part company with you on rando chest thumping on the internet, you approach the problem from the angle as you wish it to be rather than what it really is. You've mentioned on BO that you sit on the left side of the isle, fine you're choice but the problem with the Western left is that it incorrectly believes everyone else in the world in charge of other non-Western countries wants the same things for their people, has some common values with the West or can be reasoned with based on what will bring them material gain.
None of those things is inherently true. There are vast swaths of the world that don't want their people to live to well, that are not interested in peace or normal relations with the rest of the world as they need external enemies to distract their populations from the incompetence and corruption of their rule and do not in anyway respect or want to live in the "rules based order" that the West thinks is/has to be ascendant across the globe.
These people respect power and act on fear. Fear they will lose their power and/or lives. Occasionally kicking the shit out of them when they get too frisky is just an unpleasant fact of life if we wish to have a presence in their area of the world and or keep them from getting leverage over too much.
You're right we do have lots of options as a superpower but make no mistake, no one respects a strong dithering pussy. A big strong guy that allows a weaker, aggressive, loud bully to push him around doesn't actually have anyone's secret respect, they (the crowd watching) are just waiting to see what happens and to go with the winning team.
I'm not saying to just willy nilly throw power around and act like an ass around the world, but when it is time, just do it and state it was in our interest to resolve the matter favorably to our interests. No apologies, no over analyzing it.
Victory is a rationalizing force all it's own.