"I say "You shall know them by their fruits"."
But how do you know their fruits?
"The ideals of the 19th Century gave us the bloodiest Century in history."
Dubious claim. Certainly it was not even close to the bloodiest relative to population. Also, it saw dramatic drops in deaths from disease and starvation.
"Marx gave us Communism, which has a body count in the tens of millions, more than actual war."
Dubious again. I have not seen numbers claiming that communism, even if it assumes the blame for things like famines within its borders (resource mismanagement) equaled the deaths from war during the same period.
"Nietzsche gave us moral relativism,"Beyond Good and Evil" so how has that worked out?"
I have never heard of anyone killed in the name of relativism... absolutism, on the other hand...
Anyway, calling Nietzsche a relativist is a gross oversimplification. True relativism requires a "view from nowhere," something Nietzsche dismisses as impossible.
"It seems to have liberated some to be as depraved or violent as they want to be. He was a favorite in Germany in the 30s"
A selective misreading of Nietzsche was definitely a component of Nazi philosophy. For his part, Nietzsche despised the sort of crass antisemitism that the Nazis represented.
" along with Herr Heidegger."
No source, no argument. You can repeat this claim as much as you like. That will not make it true.
"Ideals have consequences."
Indeed, but we need to be intelligent in identifying them. We need to recognize extenuating circumstances, or the possibility that these ideals can be used for cynical aims.
And what about your ideals, whatever they are? What evils can be laid at their doorstep, especially if we play fast and loose with assigning blame, as you seem to with the thinkers above?