I don't like Citizens United either, but you should better inform yourself about the decision.

1. The idea of corporate personhood predates CU by over a century and the Supreme Court had already asserted that corporations enjoyed certain constitutional protections in previous decisions.

2. Far from inventing the idea, the CU decision didn't even rest on corporate personhood, but on the idea of the freedom of speech generally. The logic of the majority was that speech itself is protected, irrespective to whether the speaker is a person or an organization. The First Amendment covers individuals, but also newspapers, book publishers, radio stations, and so on, and that should extend (they said) to non-media corporations. No assertion of personhood necessary.

The problem, in my opinion, is that that conclusion combined with previous decisions that treated limits on spending as limits on speech, allowed for unlimited spending. The majority also naively asserted that independent spending posed no risk of corruption, which I think is laughable.