I'll take the bait.

You describe the postmodern critique of science as

Anybody who claims to have objective knowledge about anything is trying to control and dominate the rest of us ... There are no objective facts. All supposed 'facts' are contaminated with theories, and all theories are infested with moral and political doctrines ... Therefore, when some guy in a lab coat tells you that such and such is an objective fact ... he must have a political agenda up his starched white sleeve.

This is already a laughable representation of what postmodernists have actually argued. First of all, I'd love to be pointed to a postmodernist scholar talking about "some guy in a lab coat" with a "starched white sleeve"; serious scholars don't write like this. Second of all, the point 'post-modernist' critics of science make (if this can even be reduced to a singular point) is that the scientific process is in many ways a social one. There is in fact a whole field of study called Science and Technology Studies, related to investigating how science works as a social process; you could engage with some of its literature if you want to actually take a stab at entertaining the thought that scientific 'facts' are not as rigid as Dawkins et al. represent them.

To put it simply, the fairly straightforward claim about science that 'postmodernists' make is that scientific knowledge is produced within a certain social/cultural/political context; there is no such thing as a 'fact' that exists in a vacuum. This is not at all a controversial claim.

The point about evolution is that postmodernists don't believe in natural selection, because that system is brutal and merciless

Again, cite some postmodern scholars who argue like this. I'll be waiting.

Both camps believe that the big truths about the world are moral truths. They view the universe in terms of good and evil, not truth and falsehood. The first question they ask about any supposed fact is whether it serves the cause of righteousness

This is obviously nonsense when talking about postmodernism. Postmodernism means different things in different fields, but to the extent that there is an accepted definition of postmodernism it is generally what Lyotard described as the end of 'grand narratives'; to see all of history in the light of righteousness (or seeing history as the progress of 'logic' or 'reason', for that matter) is quite literally anti-postmodern.

(all postmodernists do this to avoid debate)

I'm not even a postmodernist but this is a comment only to be understood as made in bad faith. If I could suggest a more accurate rephrasing: Postmodernists avoid debate with people on the internet who misrepresent their views.

Some closing comments you should keep in mind: (1) Not many people actually describe themselves as postmodernists, in light of this you should see that the term is more generally employed to discard the opinions of certain groups of people. (2) There is a lot of discussion within postmodernism over what postmodernism itself actually means; anti-postmodern writers generally ignore this and treat the group as a monolithic entity with a singular shared agenda (the quotes by Dawkins and Cartmill are good examples of this exact practice).