While it can be troubling that may label just Hitler as evil and therefore dismiss the evil of the entire system built around Hitler, and indeed the world-wide connections the Nazi regime enjoyed (some prominent citizens from our own country supported the regime through various industries), you also don't want to fall into the trap of rationalizing this in a way that lets Hitler off the hook. He and the Nazi high command were still the most responsible for the atrocities of WWII in the European theater, while at the same time we can still recognize the problems with our entire Western society and humanity as a whole that allowed him to be in power or the evil men in our own societies, or the evil in us ourselves.
Most mainstream historians and scholars have not rounded it down from 6-8 million and it is still the agreed upon approximation. The people who attempt to degrade the number over time have always seem very questionable to me--they almost always have quite clear anti-semitic motivations and faulty statistics, and are a definite minority (think like 1% of historians).
For example, in Poland around 5 million Poles were killed, about half of those were Jewish. So that's already putting the number well above 1.5 million Jews, when you're not even including those from all the other various European countries.
EDIT: To me there seems to be a clear demarcation between historical warlords and modern dictators--to compare Hitler and Genghis Khan is again, somewhat letting Hitler off the hook. The social norms of the 20th century are so vastly removed from those of the 13th that attempting to rationalize Hitler's behavior by comparing him to Genghis Khan doesn't make sense to me. Germany was a modern, industrialized nation--they don't have the excuse for conquering other countries and killing millions of people, just like we don't have an excuse for our various atrocities committed in the 20th century, either.