With no hostile mods we might as well just play creative mode.
What fun is mining/exploring dungeons without some element of danger? It's already too easy to do and boring, so why make it more so?
The structures you'll make as a result will have no meaning. We look at the city we currently have and our houses, we think, god I spent ages mining a pit to make that. Or maybe you did die trying to make the structure. I think about the many trees I murdered in the middle of the night, and how many ghast dodges I did to transport the wood over to the village.
Sure it can get annoying, gathering supplies then building them. But the end result is you look at your creation and think you've earned it. No mobs is just pointless grind.