Economical and ethical issues are the kind that would be immediately swept away if, say, China said they were going to beat us there. The cost is approximately trivial compared to the US's budget. Technical issues I don't really buy. Getting to the martian surface isn't much more complicated than going to the moon and back. Getting back into martian orbit is trickier, but not in a "Requires novel breakthroughs or undiscovered science" way.

It's perfectly reasonable to say the reason we don't currently have anybody on Mars is because we (politically) just don't really want to. If the Russians had beat us to the Moon, we probably would have made it Mars decades ago.