I saw this last night, and I will say that I did not like the resolution. I understand where Tony Stark was coming from, but honestly hitting the "undo" button would have been more merciful, IMO. Some scenarios that are all too likely in "just bringing everyone back"...
A wife loses her husband (or vice-versa) to the Snap. She mourns. She moves on. Remarries... husband comes back. Now what?
Parents lose a child to the Snap. Parents end it all in overwhelming grief. Child comes back to no parents. Now what?
People overcome with the horror of the Snap get into drugs, alcohol, etc. to deal with the despair. Their lives are ruined. (This was sort of touched on with Thor, but played for comedy... this is in no way funny).
The world economy and political stability was no doubt fundamentally upended and might not recover.
Spend just a little while thinking about this, and you can come up with all kinds of nightmare scenarios for the people who survived as well as those who came back.
People across the universe, not just Earth, dealt with unimaginable trauma for five years. "Just bringing everyone back" wouldn't fix any of that.