I don't agree. This poster wasn't required to identify themselves, and that means a lot. They could have used a proxy, or used an open Wi-Fi spot.
So your argument is that as long as there remain theoretical means to protect your anonymity via technology, nothing the government does should be construed as stepping upon the right to anonymous speech? If I use Tor but the local node was ran by the NSA and they reveal my identity, there is no problem because I should have selected an anonymous proxy in Bulgaria? I suppose the freedom of religion isn't abridged if the government shuts down every church in the nation, since worshippers could meet in secret in someone's basement?
If ISPs and websites were actually required to log the information you say, then that would be an issue. But that's not the case now. Hopefully it remains that way.
I don't follow your logic here. Are you saying it is a problem if the ISP was required by law to keep the data and then the government asked for it, but would not be a problem if the ISP kept it for their own reasons and the government asked for it?