Because there will definitely be some 3rd world Marxists there. You gotta remember the history of the organization and the countries that it represents. It's not just some step-sister of the WTO. It has a particular mission and it represents the UNGA, which tends to particular views you may or may not agree with.
Look at some of their pronouncements on the Doha round. I think they do a lot of good, but I'm sympathetic to their views in many cases--you may not be. If not, you may be frustrated, if you're quite adamant about your views; however, I know a few people there and they do good work of all stripes with no problems.