A man can be disadvantaged. And there are some areas of life where, as you say, men are put at a disadvantage due to the actions of other men. This is not because "Men are second class citizens", it is a systemic issue of gendered preference that disadvantages men and women but has traditionally been a system set up to benefit men.
There are injustices in the world that are unique to men, and deserving of correction and justice. That is not in question. What is in question is looking at the state of the world and saying "You know who really has it tough? Men."