Well in this case you certainly can. Someone who doesn't want to be identified while making an argument clearly doesn't want to held accountable for their claims. But science depends on reliable sourcing and verification; someone who does't want to play by those rules can be safely ignored.
Anyway, I can make a good probable guess as to why, and it doesn't do any favours to the idea of taking him seriously.
Time is the one thing we all get at the same rate, rich and poor alike. It is too valuable to waste on a someone who advertises their own unreliability.
Maybe he is a US Senator and doesnt want his identity shown?
Maybe he is a an Allied Fan Boy, but doesnt want to be seen talking about Axis?
Or Maybe, he is talking about contravertial topic online and doesnt want that history to taint his future.
There are many reasons why people cover their identity. Listen to what is said, not the method of delivery.
AFFRS, great pics mate, keep em coming - especially the Tiger Tanks