My vote is that marriage isn't the most important issue. Bringing children in to the world is.
If people aren't planning on having kids, then it seems wise to be realistic, and plan for potential problems ahead of time. Perhaps requiring a prenup is offensive, but then resisting one is too. The couple should navigate this in any way that works for them.
Kids are a different matter. If the parties are not willing to split all assets 50/50, then they aren't in a position to have kids. To me, a prenup defines a state where the couple is committed enough to give it a try, but not committed enough to have kids.