What are you talking about? The Waffen-SS was a military unit. The main thing about it was that it not under the direct command of the Wehrmacht and that many volunteers from all over Europe were allowed to join. The Wehrmacht regular divisions were usually made up almost exclusively of German citizens.
There were, practically in all major armies, units of criminals or deviants, but this for sure doesn't apply to the Waffen-SS as a whole. For the regular units, the military training and discipline was harder, and they were better equipped. In the war they were used as "fire brigade", because of their mobility and efficiency. But this brought the units in the most dangerous of all spots with the highest losses. Some of the commanders were no professional military officers, or more fanatic and rather careless about their troopers. But that was also not a regular feature, just something more common than in the Wehrmacht.
There was of course a higher percentage of "political" people in these units, that's also sure, but more so at the beginning of the war, than in the later period, when the recruitment was expanded, the standards lowered. They were still higher than in the regular units usually (like for height, fitness etc.), but definitely no longer as high as they were before.
And all those "ethnic units" of volunteers, from all around the continent and beyond, being usually brought under the Waffen-SS, not the Wehrmacht command. So in the very end it was primarily an issue of command structure and where the recruits came from.
One of the more notorious units being this one:
https://en.wikipedia.org/wiki/Dirlewanger_Brigade
In the German armies (Wehrmacht and Waffen-SS alike), this was a true exception. "Funnily" Stalin like with the purge after the "Roehm-Putsch" in Germany took things literally and made it much bigger and worse than the Germans ever did in this respect:
https://www.jstor.org/stable/20750232
But penal brigades and stuff like that being known from many sides, in many wars. And they usually caused troubles one way or another, every time.
The Ukrainians now use mercenary units and volunteer units of similar character, I wouldn't wonder if some of the reported atrocities being more often committed by those too.