Your gear is more valuable than any likely reward gained from tangling with the Rust Monster.
This presumes that one only tangles with a rust monster in order to get the bling behind the rust monster. Either that or they are "forced" to do so.
That doesn't resemble the game experience I seek.
Sure, getting new and better gear is an element of the fun.
But so is overcoming things when under various disadvantages, such as fearing losing gear or having lost gear.
But even more important is the character's involvement in larger than life adventure.
As you express the point of "screw those children", I really see us talking about very different ideas of what makes the fun be fun. For all I know, you are having vastly more fun than me. But it is certainly different.
You don't have to be "save the children" characters to have fun playing. That implies good guy "hero" characters only. But, to me, there must be something the characters care about or have some drive to go after. And you seem to be using "save the children" as a simple placeholder for whatever accomplishment the party is after.
A separate angle on your response is: why must every monster be something you defeat? Monsters that can only be *defeated* by "nuke for orbit" can be GREAT creatures to use. I disagree with the implication that this constitutes the only sensible response. To paraphrase a friend from around here: If the DM puts a river of acid in front of the party it does not mean that the party is expected to drink it away. And if a player concludes that this is the only sensible option, then there is a real problem in mismatch between DM and player.
A *BAD DM* can screw up a game in all kinds of ways. But I'm assuming a good DM. With a good DM, you can decimate the party's supplies and resources and then throw a seemingly (or even truly) overwhelming challenge in the party's path and still create a really fun experience. But I'm also assuming the party won't try to drink the acid and won't expect every encounter to provide a material profit.