The answer in the 60s was "to beat the Soviets". Today, we are partially doing it to beat China, but we really are gearing up for Mars.
You can't just start from zero and fly to Mars. You need to build an entire workforce able to produce and operate fantastically complicated machines. And you need to fly regular missions, each more ambitious than the last, until finally we can land people on the Red Planet.
Artemis II is the beginning.
> but we really are gearing up for Mars.
Which again is cool, but useless. And actually counter-productive, because we risk contaminating Mars with organic stuff coming from the Earth.
Landing on Mars is the artifact of all of the innovation required to get to Mars. We benefit from the innovations, not the landing per se. It is far from useless
"Useless" and "counter-productive" are value judgements, not objective conclusions.
My opinion is that landing humans on Mars could be the start of a new age of exploration, which would massively benefit humanity. And the risk of contamination is worth the potential reward.
That's just my opinion, of course, but it happens to be NASA's opinion as well.
Was the Wright brothers’ first flight useless, or did it teach us lessons that lead to the Concorde and 777?
Was the first automobile so slow and clunky it was useless, or did it lead to the F1 cars of today?
Was Alan Touring’s computer so slow it was useless, or did it lead to this comment being typed on a device that is many orders of magnitude faster and smaller?
Going to Mars will teach us a lot. In the future when we go further it will be useful in ways we can’t imagine today.