Doug is correct.

Singers and musicians can hold whatever opinion they want and choose to express it during their performances, in other public areas e.g. the media and press etc. They can also be politically activists or play a supportive role in any of the above.

I've no objection to them "haranguing" an audience or even singing about subjects which I may disagree with or find offensive as long as they are not doing anything illegal.
However, they do so at their own risk in that they may alienate audiences, club organisers who might later give them a booking and so on.
If something really annoys or offends me, I certainly won't be queing up for the next gig albeit, for the most part, I don't mind having my views challenged from time to time.

What my original post was about, and the thread has certainly drifted, is that no performer should necessarily be *expected* to hold strong views on a particular subject or obliged to act on any which he or she may have within the public arena whether at a gig or elsewhere.
My example above was in relation to the Scottish Independence Referendum but I also heard similar sentiments from various quarters at the time of the Iraq War and, in fact, many other major events.

There is diffence, in my opinion between asking questions such as "Why are there no protest singers these days?" or "Where are the protest singers?" as opposed to "What about all these singers? Why aren't they protesting?"