In theory, we've had the tech to at least land people on Mars from the 70s (they'd have likely been dead bodies, but hey). Going to the moon actually makes more sense than meets the eye, and it does have resources.
1. Water exists on the moon, it isn't plentiful, but it exists. Where water exists, you can make rocket fuel. For deep space manned exploration, barring improvements in propulsion, that will be important.
2. It's beneficial to have a proving ground for new tech, like regolith 3D printing, or farming. The moon being only a few days away makes it a realistic test bed for emergent tech. In other words, you can afford to have something fail on the moon and get a replacement or a return to Earth in short order. Something like that happens on Mars, everyone could die.
3. Helium 3 exists in abundance on the moon's surface, while it doesn't here on Earth. This makes it potentially highly commercially profitable.
There are lots of other reasons, but a big one to me is the fact that we aren't likely to send people without lots of fail-safes. To me, that means we will realistically we will need essentially weigh stations in space in between here and Mars, all equipped with the ability for things like life support, supplies, and return options. I think it's far more viable (mind you not economically) to build a series of O'Neill cylinders as both research stations and lifeboats.
That isn't to say that leap in technology can't turn all this on it's head, after all, more or less we are using the same principles Robert Goddard and Werner Van Braun used. The Starship could be a game changer for a lot of reasons beyond itself, for example, the ability to get new test beds into orbit on the cheap could (and likely will) lead to new breakthrus.