> In a series of cases over the past 40 years, we have spelled out how to draw the constitutional line between the permissible goal of avoiding corruption in the political process and the impermissible desire simply to limit political speech. We have said that government regulation may not target the general gratitude a candidate may feel toward those who support him or his allies, or the political access such support may afford. “Ingratiation and access . . . are not corruption.” Citizens United v. Federal Election Comm’n, 558 U. S. 310, 360 (2010). They embody a central feature of democracy—that constituents support candidates who share their beliefs and interests, and candidates who are elected can be expected to be responsive to those concerns.
I.e. it's not corruption if LGBT rights advocates donate heavily to get Hilary Clinton elected, and it is not corruption if she is responsive to their concerns once in office. Nor does it become corruption just because you replace a viewpoint you approve of with a viewpoint you do not approve of (i.e. when you substitute "farmers" for "LGBT rights advocates").
The case itself is also much narrower than you imply. McCutcheon v. FCC involved a challenge to the aggregate contribution limit. I.e. the law that said you couldn't contribute to a 10th candidate because you hit the aggregate limit, even if you stayed under the individual contribution limit (which is currently $2,700).
The Court started with the premise that Congress could not Constitutionally preclude people from trying to influence elections, or reduce the ability of one group to influence elections in order to increase the relative influence of other groups. It acknowledged that Congress can prevent bribery, or the appearance of bribery, but held that the aggregate limit did not achieve that purpose. If giving $2,700 to 9 candidates does not create the risk of corruption, the court reasoned, how does giving $2,700 to a tenth candidate do so?
What McCutcheon did not do is overturn the individual limit. Under the Court's reasoning, the result may well have been very different if the petitioner tried to contribute $10,000,000 to the same candidate.
http://www.scotusblog.com/2014/04/divided-court-strikes-down...
That's one obvious example that specifically allows bribery as long as it is not directly a quid pro quo exchange. Buying access and influence, on the other hand, was “a central feature of democracy—that constituents support candidates who share their beliefs and interests, and candidates who are elected can be expected to be responsive to those concerns.”