I'm surprised nobody has mentioned this but one reason not to do this mission is that we have ~400 Martian samples from meteors found on Earth [1]. The fact that there's even 1 is kind of amazing to me. And this has been confirmed by multiple methods including analyzing the air bubbles trapped in the rock matching Mars's atmosphere.

Flying to Mars and then flying back is incredibly complicated and much more expensive. Rather than sending an exploratory rover or a satellite, you have to basically send an entire launch vehicle when we've never launched anything into orbit from Mars before. And it has to operate essentially autonomously (for the launch).

Even missions to get samples from comets and asteroids are far less complicated because you're not dropping into a gravity well with just enough atmosphere to cover all your stuff in dust but not enough for atmospheric braking. Mars has the exact wrong amount of atmosphere.

Obviously samples returned from Mars would be better but it diminishes the value when we already have samples here. So the huge price tag and incredible engineering complexity becomes harder to justify.

[1]: https://www.nhm.ac.uk/discover/martian-meteorites-rare-visit...