By itself, elimination of political opposition by the leaders of the country committed to making a Quantensprung of the magnitude that the Third Reich had to make, is not a crime.
It is actually a necessity as country leaders are facing problems and challenges of such an enormous magnitude that they simply can not afford any opposition. Hence it is no surprise that no quantum leap of a comparable scale (comparable to Nazi Germany that is) was achieved in a democracy.
It has been achieved by either a ruthless dictatorship (Soviet Union – twice, Nazi Germany, China, South Korea, Taiwan, etc.) or under occupation administration (post-WW2 Germany and Japan).
Democracy works (sometimes well, sometimes not so much) during periods of stability; in the times of a severe crisis (especially existential crisis) it can be outright deadly. During those times only the ruthless dictatorship can save the nation in question. In other words, to prevent the country from being destroyed, one must destroy the opposition.
Using the optimal tools and methods. Including deportation and even internment (under house arrest, in jail or even in a concentration camp) of leaders of opposition and other individuals deemed by the security agencies to be a threat to the Quantensprung. And unlike in the democratic environment, during the times of crisis it is far better to “over-detain” than to “under-detain”.
Consequently, annihilation of the opposition by the Nazis was criminal (although nowhere as criminal as the one committed by Stalin and his henchmen at exactly the same time) not because of their objective (which was absolutely necessary for the very survival of Germany), but because of the tools and methods that were used. Tools and methods that were far more brutal, murderous and criminal than necessary.
I will cover in sufficient detail the whole Nazi project of eliminating the opposition (including the infamous Night of the Long Knives) in the chapter devoted to Hitler’s crimes. In this section I will only briefly cover the four key tools used by the Nazis – the Sturmabteilung (SA) paramilitaries, secret political police (Gestapo), detention centers (concentration camps) and special political courts (Sondergerichte).
Contrary to a popular misconception, in just about all their peacetime endeavors (with the exception of those related to their “racial” and “Jewish” questions) were highly pragmatic.
Consequently, they understood that (a) positive motivation was far more powerful than the negative one; and (b) an ounce of prevention (of anti-Nazi activities) is far more valuable than a ton of punishment.
Hence in their management of their German subject they put emphasis on positive stimuli (i.e. on propaganda and actually caring for the German people by identifying their needs) rather than on a negative one (fear of being punished by the Nazis).
And the fundamental objective of their political repression system was to prevent anti-Nazi activities from happening in the first place rather than to punish the “wrongdoers”.
Consequently, the primary function of the SA (until they were relegated to political oblivion in July 1934), Gestapo, concentration camps and special courts was intimidation, not punishment of actual or potential political opponents.
Historians generally agree that these instruments of intimidation (especially the much-feared Sondergerichte) performed their functions very well and had a strong deterrent effect against active opposition to the Nazis. The latter appears to be was sufficiently intimidated through psychological terror to refrain from active (or even passive) resistance to the Nazis.
The Sturmabteilung (SA) was the only “terror and intimidation” tool (and a very efficient one at that) used by the Nazis prior to their acquisition of absolute power in the end March of 1933.
Nazi stormtroopers beat up their political opponents; prevented, disrupted and dispersed meetings and rallies; attacked and destroyed the premises (headquarters and branches) of political parties; kidnapped and detained opposition activists (by the time Nazis came to power, the SA operated a vast network of illegal detention centers).
After the Nazis had obtained the absolute (plenary) powers in Germany after the Reichstag Fire Decree and especially the Enabling Act became laws, they no longer needed the SA to suppress the opposition. Now they had the whole law enforcement system of Germany (police, prosecutors, the courts and the penitentiary system) to do this job for them.
Actually, this was the primary reason for the spectacular fall of the SA in 1934 – they simply had nothing to do any more. Their last valuable contribution to Nazi cause was made weeks before the Enabling Act – just before the March 1933 elections (the last multi-party elections in a unified Germany until 1990).
The SA unleashed a nationwide campaign of violence against the Communists, Social Democrats, other left-wingers, trade unionists and even the centrists. Which, however, did not achieve the desired outcome – Nazis still got only 44% of the votes (still short of an absolute majority).
After the Night of the Long Knives when just about all SA leaders were either murdered or incarcerated, SA functions were reduced to just one – attacks on the Jews.
For over four years, the Brownshirts were the main perpetrators of anti-Jewish violence which culminated on the infamous Kristallnacht in November of 1938.
After the murder of German diplomat Ernst vom Rath on November 7th by Herschel Grynszpan (a Polish Jew), the SA were used for “spontaneous demonstrations” against this very much terrorist act (which, however, does not justify the subsequent pogrom at all).
In very violent riots, the stormtroopers shattered the glass storefronts of about 7,500 Jewish stores and businesses (hence the name Kristallnacht – “Crystal Night”) given to the events. Jewish homes were ransacked throughout Germany.
Members of the SA and SS (and a lot of “ordinary Germans” who participated in the event en masse) damaged and in many cases destroyed, about 200 synagogues (nearly all Germany had), dozens of Jewish cemeteries, more than 7,000 Jewish shops, and 29 department stores. Dozens of Jews were beaten to death and more than 30,000 Jewish men were arrested and taken to now very much legal concentration camps (just about all of them were soon released).
Thereafter, the SA predictably became overshadowed by the SS, and by 1939 had little (if any) remaining significance in the Nazi Party and in the Third Reich in general.