The question of why so many Germans voted for Hitler is a BIG question, but the second question, the lenient sentence for the Beer Hall Putsch, is easier to tackle.

From an earlier answer of mine

The slap on the wrist that Hitler and his co-defendants received was the byproduct of the Weimar judicial system that was dominated by conservative nationalists whose careers began under the Kaiserreich. The trial's chief presiding judge, Georg Neithardt, was a noted conservative and had an established pattern of giving harder sentences for left-wing political crimes and lighter ones for crimes committed by the right. He had already given Hitler a lenient sentence in 1922 for stirring up a riot. The chief judge treated the defendant Erich Ludendorff with extreme deference, even reportedly said before the trial that the former general would be acquitted because Germany still needed him. Neihardt allowed Ludendorff to replace an earlier interrogation which demonstrated his knowledge of the coup with one that suggested he was ignorant of the enterprise's treasonable details. Neihardt's fellow judges were also quite sympathetic to nationalist causes and thus more amenable to lenient sentences. Hitler would later claim that the lay judges would only convict Hitler and the other defendants (minus Ludendorff whose wartime deeds had put him above reproach) if they were given a mild sentence with the possibility of early parole.

The political biases of the judges dovetailed with the general disinterest on the part of the prosecution to try Hitler to the fullest extent of the law. The chief prosecutor Ludwig Stenglein was a man disinclined for direct conflict which made him a poor choice for the trial, which soon devolved into a media circus as the judges allowed Hitler free reign over the courtroom proceedings. The Bavarian state government wished for the trial to go away quickly in no small measure because a lengthy trial could expose the involvement of the NSDAP and the Bavarian State Police and the Reichswehr before the Putsch. This further constrained the number of witnesses that the prosecution could call to the stand and the state did not attempt a thorough investigation for more incriminating evidence against the defendants. Stenglein's plea statement included a paean to Hitler's patriotism and praised Hitler's sincerity in the struggle against international Marxism.

The light sentences for Hitler and Ludendorff's acquittal did not go unnoticed in the German press and created a scandal as it gave Hitler a national platform at very little personal cost to himself. Even Neithardt admitted to one of the prosecutors that letting Hitler harangue the courtroom for four-hour stretches was something of a mistake. Despite his earlier claims of Hitler's fidelity to Germany, Stenglein tried to ensure that Hitler served his full term and pointed out during the parole process the gravity of Hitler's crimes and his poor conduct in Landsberg, but the Bavarian Supreme Court was no more willing listen to these very serious indictments than their colleagues in the earlier criminal trial.

Hitler himself called his stay at Landsberg "my university paid by the state," which was emblematic of how he flaunted the rules of the prison. Hitler allowed his visitors to smuggle out letters, which was a violation of the prison's already lenient rules. It was also quite clear from the available evidence that Hitler was planning on reconstituting the NSDAP's paramilitary arm once released, which would have been a violation of the law. The prison governor, Otto Leybold, was another fellow-traveler sympathetic to Hitler and he often turned a blind-eye to Hitler's violations of the prison's rules and undercut attempts to have Hitler serve his full term.

So in this context, the bad conduct Stenglein referred to was Hitler was being disingenuous when petitioning for early release. He had not reformed in a significant fashion and he exploited the already lax rules of Landsberg to hold court among both his fellow inmates and his visitors (Otto Strasser would later claim in his memoirs that he had a "Machiavellian" idea to convince Hitler he should write Mein Kampf just so Hitler would shut up and leave his fellow prisoners in peace). The evidence that Hitler was still corresponding in secret with paramilitary and other figures in the Bavarian right demonstrated that he still was a danger to German society and had no real intention of not resuming his assault against the Republic. Even though Hitler proceeded to use legal (and some not so legal) means to achieve power after his release, this was not readily apparent at the time.

Sources

Gordon, Harold J. Hitler and the Beer Hall Putsch. Princeton: Princeton University Press, 1972.

Kershaw, Ian. Hitler 1889-1936: Hubris. New York: Norton, 1999.