Sure as god made little green apples, give a government a list of gun owners and the government will find a reason to use that list to round up the guns. It's happening in California even as we speak.
"Oh, Tamara," you say, "but it was illegal for these people to own guns!" Yeah, today it's a boilerplate restraining order, tomorrow a Prozac prescription, the day after will be membership in unpopular political or religious groups, and next week it'll be unpaid parking tickets. Once the .gov has a list of where the guns are, all they have to do is tinker with the requirements of ownership and they can round up as many as they want.
Registration leads to confiscation, with 100% correlation.
Each and every place, each and every time.