When people try Coke and Pepsi without knowing which one's which, they show a widespread preference for Pepsi, which is demonstrated in their brain activity (specifically, in the ventral putamen). But if you tell people which one's which before they drink it, the majority prefers Coke. These experiment subjects did not have the same sensory experience as the others and then give a biased report of it - they actually had a different sensory experience, again demonstrated in their brain activity. This famous experiment by Read Montague shows the power of brand influence on our experiences.
Taste in music is equally subject to external pressures. When asked to download and rate unknown songs, choices are affected by social influence. When people are aware of which songs are heavily downloaded and highly regarded, they are more likely to download and then rate those songs highly.
Needless to say, moral intuitions are no more stable than these other subjective judgments.
These experiments also show the power of branding. In Change of Heart, Nick Cooney writes about realizing he had to normalize his physical appearance in order to be more socially persuasive. Whether or not people should judge you based on your appearance, people do, and altruists need to be conscious of that. Get your appearance straight and the halo effect kicks in, making your message more appealing.
Not only is physical appearance important, but so is your brand. The New Atheists are branded by many as strident, arrogant, and close-minded. Whether or not these charges are true, this image limits what they're able to accomplish. Political activists are often branded as violent, radical, overly antagonistic, needlessly belligerent, and aggressive. Far-left, drug legalization, and environmental activists are often branded as hippies, tree-huggers, slackers, etc. It's important for activists to be aware of how they're being perceived because those perceptions have everything to do with the effectiveness of their campaigns.