The Enterprise-D was a symbol of life in the Federation of that era. They enjoyed decades of prosperity and relative peace, and the design philosophy of the Galaxy class reflected that.

The Enterprise was built for deep space exploration and was (in theory) supposed to be deployed for years at a time without returning to Earth. The designers wanted it to be comfortable, and Starfleet personnel wanted their families to be with them on those long haul missions.

Being a major power in their part of their galaxy that was technologically advanced and at relative peace with other major powers, they were a little full of themselves.

Not long after its mission started Starfleet began encountering forces like the Borg and the Dominion, and they realized they weren't quite as untouchable as they thought. This became a major theme both in-universe and in the real world.

These kids don't traumatize themselves, gotta do something since all of Earth's problems are solved

Head canon: In times of infinite abundance, people prefer a glorious death to an easy life, even for their children.

One of these days I'm gonna have to read the whole thing myself, but in the first few pages the ST:TMP novelization, Roddenberry himself sort of says that Starfleet is full of deeply conservative throwbacks who have a weird combination of wanderlust and tolerance for authority that life on post-scarcity Earth cannot satisfy, and that both they and the Earthbound population are happier with Starfleet personnel being off-planet.

It strikes me as a hand-wavey way to justify to himself how he can have a free-love, no-money utopian society, yet all the media he could manage to get made is basically showing us a combination of NASA and the US Navy, with a pretty marked tendency towards the latter. For Gene, any 23rd-century people whom 20th-century minds could even comprehend would have to be psychological Luddites.

It would be like if Columbus in 1492 decided to go exploring the far unknown ocean and asked all his crew to bring along their families because they would all be gone for a long while .... what could go wrong?

They're hoping Geordi LaForge is in command - he ordered the only saucer separation where the intention was to safely preserve the civilians, and where the separation itself wasn't an untested dangerous high-warp maneuver. (The Arsenal of Freedom)

Riker, on the other hand, separated the saucer in order to shoot at a Borg cube from two directions at once. (The Best of Both Worlds)

Picard is the one who wouldn't drop out of warp to do the separation. (Encounter at Farpoint)

Riker also ordered saucer separation after a warp core breach was in progress and unstoppable. (Generations)

Those were the only four times the Enterprise-D was shown to separate.