If it was a criminal case, you'd have real 4th-Amendment and 1st-Amendment issues. As it is, we're talking about a civil matter, and those constraints don't apply to non-state plaintiffs.
Judge Collyer isn't breaking new ground here- it's generally accepted by US courts that individuals can have no expectation that information they freely give to other persons is "private." I think one of the problems here is that people are confusing "personal" with "private." Your personal information is not necessarily "private," in either the ordinary sense or in the technical legal sense.
Your name is not private. Your street address is not private. Your vehicle license plate number is not private. In many states, your driver's license number and your driving records are not private.
In this case, the USCG is asking the ISP to give up the names and mailing addresses of people who were using certain IP addresses at a given time on a given date. Since names and mailing addresses are not private, neither the ISP nor the people using those addresses can claim "privacy" as a reason not to comply with this request.
That's just how it is. People who are reacting to this with surprise are wrong to blame the judge in this case- her ruling was made according to well-settled law. She cited this portion of her analysis to cases in the 4th and 6th circuit courts of appeals, and there are similar decisions from several of the other circuits as well.
You can read the whole order here: Order denying motion to quash.
Now, if the question was whether your ISP could turn over your DNS logs, effectively showing the list of sites you were connected to and the dates and times of connection... well, that's a very different sort of thing.
(why yes, I am a lawyer working on some of these cases).