For clarification: what makes you believe that denying the Armenian Genocide is "widely accepted"?

There are a few differences between Holocaust denial and denial of the Armenian Genocide.

The first is that Turkey doesn't actually deny that the actions took place. They accept that Armenians were rounded up and killed, they accept that there were death marches in the desert etc. etc. or at least for the most part they accept these things. The bit that Turkey denies is that it was an attempt to eradicate the Armenians as an ethnicity and culture. IIRC correctly they view it as ethnic cleansing. In comparison Holocaust deniers tend to deny that it happened at all.

The second and most important difference is that the Ottomans were partially justified in their suspicion of the Armenians, there were Armenians from within the Empire that signed up to fight with the Russians, there were also Armenian uprisings during the war.

The third and final difference is that the Armenian massacre took place on the wrong side of the Bosphorus to be truly shocking for the west.