>>> Our country doesn't have a tradition of unlimited anonymous election spending.
I'm pretty sure it does - people always donated to causes, and before the current "money in politics" panic campaign, they were anonymous for the most part. All the statutes requiring donor disclosure that I could find were pretty new. Could you bring an example of donor disclosure requirements that would qualify as "tradition"?
>>> That only started happening with Citizens United in 2010
Citizens United decision changed very little on establishing privacy or disclosure. The decision was that the government can not ban a group of people, organized as a company, labor union or any other association. It actually upheld the disclosure requirements of BRCA. Of course, since the group has no obligation to disclose its membership or revenue sources, it can be used as a vehicle for anonymous speech. But that venue always existed, it was just that BRCA unconstitutionally banned companies from political speech.
<i>You value privacy over transparency. I do in some areas, but not in political spending.</i>
It's not the question of my values. I won't be the one who would abuse disclosure requirements. It's not the question of my preferences, it's a question of consequences which would happen regardless of what you and I prefer. Ignoring this consequences because they don't align with your values won't make them go away, they still will happen. Powerful people would still abuse disclosure requirements to suppress their opponents and ruin their supporter base, regardless of what you think about it.
It's like Myspace saying "we value user experience, so we won't implement restrictive XSS filters". Then a guy named Samy comes and writes some JS code and pretty soon he owns their user experience lock, stock and barrel. Did their values help them prevent it? Not really. Now, in this case the effect is a bunch of wrong bits on the internet and a couple of mildly bruised egos. But with political campaign abuse the result would be bad laws passed, bad people elected and lives of people ruined when they opposed some bad candidate.