The voice within.
When, during an interview, the band's front man said that he sings "from the heart," nobody thought anything of it. The remark was considered to be a stupid cliché, and most ignored it altogether in favor of discussing his comment in which he likened chicken fingers to genocide.
No one considered it to mean that the words he sings are not his own, that they belong to his heart, or more specifically, an alien parasite living in his heart, an alien parasite who had overtaken his body many years before, and that the stupid comments like the one about chicken fingers were only meant as a distraction so that no one would ever question the logic of his actions, thus leaving the parasite free to enact his evil plot to dry up all the world's oceans.
Which is to say, no one considered the truth.