Even without getting into mystical considerations like whether Aharon’s participation gave the eigel certain powers or animation, think practically of the public relations coup his participation led to. “What do you mean you don’t want to be part of the eigel movement? I have here a signed haskamah from none other than Aharon himself declaring, ‘Chag la’Hashem machar!’”
This is our society today. It’s not enough for some people to run around and advocate all kinds of nonsense, but they also have to shlep in the Aharon haKohen’s of our time, or the memory of Aharon haKohen's whom they said would condone their approach, to give themselves legitimacy. This invites one of two responses: 1) those who go ahead and worship eigels, convinced that either they are not really eigels or eigel worship is OK because there is some proclamation that sounds like Aharon haKohen sanctioned it; 2) those who wrap themselves in a mantle of righteous zealousness and use the opportunity to rip apart not eigel worship, but to rip apart our modern day Aharon haKohen’s, never once pausing to consider that there is more to what is going on than meets the eye.