All of what you say is quite true.
Postmodernists believe that Western culture is just a social construct, but going by the standards and beliefs acticulated by Postmodernists, Postmodernism itself can be seen as just another ‘arbitrary social construction’ like all other ideologies.
As stated previosuly in the link in the first post, Postmodernists believe that their tenets are absolute...while they relativize everything else.
In which case, it has no more validity than any other, so we white, capitalist (I wish), Christian Protestant, Euro-centric males, have no reason to assist its followers in their goals.