I’ll agree that it would be difficult, expensive and dangerous. Impossible isn’t a word I would use lightly.
I imagine it would be very difficult. Getting to the moon was all about weight. Getting to Mars with a lander that could carry enough fuel to escape the planet’s gravity for a return trip would presumably mean a larger rocket than the Saturn V. If you aren’t planning to bring back the explorers, I suppose that makes it easier. I’m nobody’s rocket scientist though. :)
The moon has 1/6 the gravity of Earth, but Mars has 38 percent of Earth’s gravity. That seems like a lot of fuel a lander would have to carry to return astronauts to Earth.