Adolf Hitler needed a paramilitary wing for his party for a number of reasons. First and foremost, he needed his own (i.e., loyal only to him personally) paramilitary force to successfully execute the coup without having to rely on Bavarian Army – Reichswehr units, Freikorps and the Civil Guard (their neutrality would be sufficient). The failed Beer Hall putsch proved it beyond the reasonable doubt.
A unique feature of the German political scene (that it owed to a whole series of bloody coups and uprisings – Spartacus uprising, Bavarian Soviet Republic, Kapp Putsch, Ruhr Uprising, etc.) was its acceptance of a high level of political violence. Which by mid-1920 most (if not just about all) Germans considered natural.
Natural and even necessary – Germans (especially Bavarians) sincerely believed that the return to “law, order and normalcy” can be achieved only by violence. Either “from the top” – by violence perpetrated by government forces (police and Reichswehr units) or “from the side” (by Freikorps and other non-government paramilitary units).
This belief, which got surprisingly deep surprisingly fast did not go away after the demise of Weimar Republic. On the contrary, it got even stronger – which explains why most (if not overwhelming majority) of Germans accepted (and even supported) violent suppression of political opponents and persecution of Jews by the Nazis (as well as their brutality on German-occupied territories).
Consequently, it is no surprise that both Left and Right parties (both no strangers to violence) established paramilitary units and used them on every suitable occasions to intimidate, assault (and sometimes even murder) their political opponents, disrupt their meetings (and, of course, protect themselves and their events from their political enemies).
Hence, to survive (let alone succeed) in this highly violent environment, NSDAP had to develop not just similar, but superior paramilitary capabilities.
However, there was another – very personal – reason why Adolf Hitler created a powerful paramilitary wing of his (now his and his alone) political party. A military environment was the only one where he was emotionally comfortable.
And although NSDAP was now his absolute dictatorship, the Führer’s party, it was still a purely civilian outfit. And he desperately (really desperately) needed a military (or at least a paramilitary) one.
And, being fiercely intolerant of any competition, he wanted his paramilitary force to ultimately replace all (very much numerous) right-wing nationalist paramilitaries (which he subsequently did).