Why is the Armenian genocide so controversial?

Because it is not a genocide but a mutual mass murder and is being advertised as fake news with forged documentaries by some heavily Armenian-biased writers.

Explanation:

On one hand you have a solid research information which says that it was a genocidal act to get rid of the Armenian population, while the (political) acknowledgement of the same knowledge lags behind considerably. This disparity creates a gap in the politics of memory, a process which is not only used by different actors in a society, but also highly affects and creates our national identity and narrative, our relations with law and justice and finally the path towards reconciliation.

As Turkey has denied the allegations for any wrongdoing to escape liability (issue of punishment and reparation stipulated in the Sèvres Traty, 1920), the history revisionism had created an alternative narrative which has only widened the perceived reality in the eyes of the Turkish society. This view has, however, started to crack as information online but also through publications and debates to disseminate among Turkish citizens. Nonetheless, the revisionist version taught to 4–5 generations is hard to change, not to mention the psychological barrier the present-day Turks have to surmount when faced with an image which would clearly be regarded as defamation of past generation , especially the founders of the republic. From an international point of view, the controversy has heightened even more lately as world leaders refraining to recognize the events by the true name no longer deny the genocide, but rather bluntly refer to the importance of their relations with Turkey instead. Thus, the same disparity between knowledge and acknowledgment underlines an apparent disrespect for not only scholarly research and facts in general, but human rights in specific as these are sacrificed for realpolitik considerations; a trademark not exclusive for the Armenian case, but sadly enough in general regarding human rights in our age and time.

the constitution gives congress the power to regulate commerce "among" the several states.