Seriously, I guess people said the same thing about Columbus in 1492, Zheng He in 1413, and Leif Erickson and his father in the first millennium. The point is discovery and expansion of the human race.
Man will get to Mars, some day. Do you want that man to be from the USA or China?
First I disagree with you as to the probability and desirability of putting men on Mars, BUT leaving that aside for the moment, If the choice comes down to my paying for it or the Chinese paying for it, then let the Chinese waste their money.
Mars consists, unsurprisingly, of rocks and dirt. How much more taxpayer money should we spend to confirm this basic observation?
There is a little thing called the "Periodic Table of Elements" that dictates what we will find any place in the universe. (Hint - the answer will always be rocks and dirt as dictated by the interactions of the elements in the periodic table)