You do not need to explicitly request it. It is implied: when you post, you open yourself up for criticism. Constructive criticism makes us better posters. Anneinside criticized me the other day for assuming that depression is more widespread in the industrialized world, and I stood corrected: I do not have data, I was acting on a mere assumption that the added stress created by industrialization boosts depression statistics; I was forgetting that in underdeveloped countries depression is underdx'd which does not mean non-existent, and I was demoting the stress of food scarcity, water scarcity, armed conflict etc. - the real stress of underdeveloped nations. That is what Anne made me see. So now I will think better before I post, I will care more about data, and try to make my arguments watertight.