These people are your heroes. So when they are like "we are going out there and we are going to beat Galactus"....yep I believe them. And then they come back with "we don't know how to save us....well actually we do, with the sacrifice of 1 life we can save our entire race"True. But it's not like the F4 just said "Nope. Guess you're all going to die". They said "Nope, we're going to find another solution". Which they obviously did.
and when they refuse to do it, you of course believe they have a brilliant plan, a foolproof scheme. These are your hereos, and you are ready to believe. And they have nothing...they have to think about it.
But they are your heroes and you believe. And they come up with a plan, a crazy over the top plan that has so much risk no sane person would ever sign off on it except for "we have to". If Reed had been even slightly wrong in his calculations, earth is gone. So you invest trillions of dollars that was going to fight cancer or world hunger or whatever problems they got, that almost certainly killed several people (there is no scenario where they build something of that scale that quickly without some people dying for it), and you go for this hail mary because its the freakin Fantastic Four, and you believe.
And then the plan goes to crap, the enemy destroys it before it even begins. Ok we tried our best, but its time to throw in the towel and attempt a parlay with Galactus. Does the FF4 do that?.... oh no, another crazy scheme with huge risk and whose failure means the destruction of the planet.
The FF4 are heroes yes...but they are not gods, and they have no right, not for one child....not for anyone. They are heroes no longer.