There are plenty of legitimate anti-pseudonymity arguments I can think of. I just currently stand on the pro-pseudonymity side and don't feel like making arguments against my own position. But possibly the lack of investment hypothesis is valid. After all, I think people (at least, people who don't think about it too hard) feel that they can tell a "real" name from a "fake" name better than some computer algorithm, and can always choose only to pay attention to people with "real" names.
Myself, I've found taking people at face value -- even when they strongly telegraph that they are not exactly as they present -- to be a rewarding approach to the internet. I'm more careful when RL gets involved.