Do you always make assumptions based on nothing but the conjecture within your own imagination? Frequently, there is an opportunity to see the replies from others to the deleted posts (replies that obviously occurred before the post was deleted). From these replies it is usually quite apparent that the post was inflammatory, vulgar, racist, or otherwise offensive -- and not a well-articulated liberal argument that the conservatives couldn't handle.
The numerous examples of argument or debate that survive the moderators around here illustrate the absurdity of your stated assumption.
Ha, since I explained how I derived that opinion (from observation of posts before they were deleted) your own assumption is found wanting. Sweet. :-)