What other information might be useful for employees or consumers? How about meetings between heads of companies discussing the fact that they're going to merge & dump a bunch of jobs? How about if they discuss killing an opposition leader in a 3rd world country so they don't get in the way of their drilling operations? How about if they are colluding with other companies within the same sector? How about if they're punishing or threatening certain partners for using an alternative company? How about if they're selling bogus investment products & laughing over the stupid people who buy them? So if they're not going to disclose these things, why should they disclose who they're giving money to?
I think this hits on exactly why "free market" principles fail, because it assumes that information is easily available for consumers or employees to make informed choices or that those consumers even care to be informed or are smart enough to understand the information that is available.
Frankly no one should be able to directly fund the campaign of a public official. They should get a set allotment from a general election fund, mandates by the FCC to allow for equal airtime & televised debates. There should be absolutely no "gift giving" or pampering by any entity towards a public official. Lobbying should be banned or restricted greatly... Etc..etc..etc.. There should also be a mandatory 3 - 5 political parties which receive funding.