He is a respected member of the community and knows his stuff* regarding privacy. I've read (some of) his posts and I've learned quite a bit. Now... he has certain preferences regarding bitcoin vs altcoins and he has a certain philosophy that he has expressed as to why bitcoin-based clones are redundant, scummy, evil or whatever. Apparently any bitcoin-based coin doesn't interest him hence the zerocash and bytecoin mentions (which are near-DOA themselves due to their problems and ...security assumptions).
He kind'a took the wrong turn in the coinjoin thread when he trashed drk and then complained that this is only technological stuff etc etc (which, in a way, it wasn't as the not-so-veiled criticism was there) in which others shouldn't post fanboy messages etc etc, but he rectified it to some extent by taking that discussion elsewhere.
* Some of the points he made though, like Darkcoin = centralized due to closed source, was like "what the..." It's not like this is an inherent property - rather a short term situation until the code is final. Almost personal-level criticism I've read about the darkcoin developers has also been uncalled for in some of his past posts. If Satoshi was around he'd tell him to cool down and that this is the nature of opensource. If someone wants to build something on top of Bitcoin he can. If he wants to build something in parallel to Bitcoin, he can also. Why the need to go to extremes to protect Bitcoin against altcoins? Satoshi would probably say "if Bitcoin is somehow vulnerable to altcoins, maybe it's because it doesn't do as good of a job" and I doubt he would get very emotional about it. No matter how one looks at that, once again DRK shows why it's the Platinum (=potent catalyst + rare / great store of value), by catalyzing the whole altcoin field towards the pursuit of privacy and anonymity. Even Bitcoin must now catch-up, with things like Dark Wallet.