What "obvious reasons?" The fact that socialist theory and history from socialists actually building socialism happens to back up their reasoning in most cases? There's also critique and discussion of problems in existing socialism coming from AES countries as well. This is an utterly self-defeating argument that only validates those most removed from the actual practice of building socialism.
Again, to stress, your point is that we should inherently distrust those building socialism in real life, and only accept theory from those that are utterely disengaged from practice.
Further, there's no critical examination of the merits of socialist theory and history produced by socialist countries on your part, the very fact that they are produced by the people actively building socialism is enough to discredit them in your views. Can you not see the logical trap? If you succeeded in building socialism and spoke about your experiences, successes, and failures, you would have to discredit yourself as fanfiction!
Should the merit of theory not be tested through practice?