Ok, let's look at your 2 claims here.
A) So, you've decided to completely abandon the "just cause" part of your argument? North Korea doing ballistic missile tests, developing nuclear weapons and threatening their neighbors repeatedly was not "just cause?" Nor was Iran attacking the shipping and oil fields of our allies or them attacking and burning down a US embassy or killing an American contractor? None of these are just causes at all huh? Well, that's an interesting argument. "You shouldn't threaten anyone but burning down their embassy, killing their citizens and funding terrorism, those are fine."
B) Trump "backed down" from Iran? Ok, I'll accept that you are 100% uninformed as to what happened. It's probably not your fault, you probably watched MSNBC or something. Not only did Iran INTENTIONALLY miss every US target is this staged "attack," they even went so far as to WARN our allies (and thereby us) an hour in advance that this was happening to make sure no American got hurt. Why? Because they needed to save face but did not want to face retaliation if they accidentally killed anyone. And how COMPLETELY has Iran backed down? They even made a point of saying, Ok, that's it. That was our "revenge." We'll stop all this crap now if you don't retaliate. AND they are now talking about the complete disbanding of the group that lead the attack against the US Embassy in the first place.
Refusing to stomp on the throat of an enemy who is surrendering is not weakness it's common sense if you aren't interested on going to war. It is utterly insane how propagandized you are. It's actually a little scary.