But we do have manned missions to other celestial bodies, and we have sent and landed probes on Mars. I'm confused as to how a manned mission to Mars is "entirely speculation".
>no precedent to assume it ever becomes possible
This isn't a qualifier for what is possible. We knew it was possible to go to the moon before there was precedent. If anything, you calling it impossible is pure speculation. OP is right, difficult is not the same as impossible.
But based on what I know, I don't see any reason to believe a manned mission to Mars is impossible with current technology.
Do you have specific reasons we can't, or examples of technological gaps?
- One year enduring radiation sickness.
- various strategies to block incoming cosmic rays: https://en.m.wikipedia.org/wiki/Effects_of_ionizing_radiatio.... In particular, hydrogen-rich plastics.
Probes aren't space travel for humans.
> A manned mission to Mars is entirely feasible with current technology.
As no manned missions to Mars have ever proven this conjecture, it is still entirely speculation on your part.
> A manned mission to another solar system is going to be very-very difficult, we'd need generational space ship/habitats. Note that difficult is not the same as impossible.
No, it is impossible. Humans cannot survive in space that long. Never have, currently can't, and there's no precedent to assume it ever becomes possible. Pure speculation on your part.