Why? Just because? Only reason I can see--at the present time--to have manned flights is to discover the effects of it on humans. Robots can do any other scientific research faster and much, much cheaper.
Initially telescopes, both visual and radio, would be ideally positioned in the airless low gravity environment. The Far Side would especially help radio observations. The low-gravity would make maintenance operations vastly easier than the current situation with Hubble and its currently unbuilt successor.
Furthermore, the moon would make a good way-station for launching and manufacture of deep-space manned probes to the rest of the solar system and beyond. The soil is chock full of titanium. Solar smelters would allow feasibility for its production in usable form. Welding of titanium requires an airless environment. A manufacturing colony would then be able to do the gross module fuselages, assembly and fittings. The rest could be lifted from earth using the Big Dumb Boosters into parking orbits then ferried up on unmanned ionic-thrust transfer vehicles.
Clearly not true. We can design individual tools to do individual jobs, but we can't design and deploy a general purpose scientific instrument that can react to new facts on the scene. We have to design and send an entirely new device in most cases. And forget it if something goes wrong. I somehow think an astronaut could have yanked on the "umbrella" antenna of the Galileo if they'd been along for the ride.
More importantly just because isn't a rational position and worthy of debate. We need to get out there in order to establish a presence other than on earth for our species. We CAN'T stay here much longer, relatively speaking. We'll either kill off the ecosystem or it will kill us, or some external force will kill us both off. We have to go on to the next environment and make it ours, or we need to curl up and die. I prefer to go on. Now, do we need to do that Tuesday? Only to satisfy my own impatience, and to make sure that the folks that go speak english and not mandarin or hindi.