Eugene Volokh discusses Bland v. Robets (EDVA) which holds that liking something on Facebook does not qualify as expressive conduct:

[Past First Amendment precedents] differ markedly from the case at hand in one crucial way: Both [precedents] involved actual statements. No such statements exist in this case. Simply liking a Facebook page is insufficient. It is not the kind of substantive statement that has previously warranted constitutional protection. The Court will not attempt to infer the actual content of Carter’s posts from one click of a button on Adams’ Facebook page. For the Court to assume that the Plaintiffs made some specific statement without evidence of such statements is improper. Facebook posts can be considered matters of public concern; however, the Court does not believe Plaintiffs Carter and McCoy have alleged sufficient speech to garner First Amendment protection.

Eugene thinks this outcome is wrong.

That’s not right: A Facebook “like” is a means of conveying a message of support for the thing you’re liking. That’s the whole point of the “like” button; that’s what people intend by clicking “like,” and that’s what viewers will perceive. Moreover, the allegation is that the employees were fired precisely because the Sheriff disapproved of the message the “like” conveyed. I would treat “liking” as verbal expression — though it takes just one mouse-click, it publishes to the world text that says that you like something.

I take a slightly different perspective. For years, Facebook users have clamored for a “dislike” button. If there is something on Facebook that you enjoy or appreciate, you like it. If there is something on Facebook you disapprove of, your only options are to like it, or do nothing. Doing nothing is not fun. Some people click like, and then explain why they *don’t* like it. I don’t know that the “like” button signifies approval. I don’t know that it signifies anything. Sometimes I will like something, or more accurately “subscribe” something to follow it, so I can keep tabs on it. This has nothing to do with whether I like it or not, or whether I am engaging in speech or not.

And what about Twitter? Following–the equivalent of liking–just means you want to follow someone. It doesn’t mean you like or dislike, or agree or disagree with someone. I follow a lot of people I do not usually agree with just to see what the competing arguments are.

Eugene is probably right, but looking at how people use these social media functions complicates the calculus a bit.