Related question: how central to Nazi policy was anti-Semitism prior to WWII?

When I vote I usually have to vote for a party that has some policies I don't like. Could someone voting for the Nazis in 1933 be forgiven for the extreme anti-Semitic policies that followed? Or was it clear what Hitler was planning all along?

Hitler had been rather clear about his anti-Semitism since as early as 1920. Once the Nazi's came to power in 1933, they were quick to institute a number of restrictions on the Jewish population of Germany. Since Jews had only been emancipated in Germany (the various German states at the time) since around the middle of the nineteenth century, the roll back of Jewish freedoms was not all that radical of a move. Many historians argue that there was a pervasive, low-intensity anti-Semitism permeating most of German society prior to the rise of Nazis, which prevented the German population from rising up to defend the Jews. Germany also had a relatively small Jewish population prior to WWII, approximately 525,000. Many Germans would not know a Jew, at least not on a personal basis. Naturally, Germans married to Jews were usually opposed to Nazi policies, but had little recourse and were themselves restricted by the regime. Most of the Jews killed in the Holocaust were Polish or Russian, who number in the millions. Once the Nazis gained power, the media was increasingly under their control. Overwhelming amounts of propaganda denouncing the Jews were also quite effective in neutralizing dissent against the Nazi anti-Semitic positions. Some dissidents, along with some Jews, left Germany after restrictions on Jews were implemented.

That being said, the Nazis were wary of popular opinion. When Hitler attempted to violently and publicly attack Jewish populations through the Night of Broken Glass (Kristallnacht) in 1938, the German people were put off by the public disorder and demonstrated to the Nazis that any Final Solution would need to be relatively discreet about the ultimate fate of the Jews.

Some historians argue that Hitler was clear and obvious about the ultimate fate of the Jews from an early date. Words that were frequently used were ausrottung and vernichtung meaning annihilation or extermination. The level of ambiguity used is debatable, but it is my personal opinion that the Nazis were particularly skilled at using just the right amount of ambiguity to allow listeners to interpret, but still claim that they were being clear about their intentions.

As for the related question, it is important to remember that the Nazi party never achieved more than about a third of the popular vote, although that is not negligible in a multiparty system. Hitler was appointed Chancellor through an alliance with the traditional conservative elites. Once Hitler was in power, however, the traditional elites could not check his power and the Nazi party came to control the state.

I recommend The Origins of Nazi Genocide by Henry Friedlander, Nazi Germany and the Jews by Saul Friedlander, and The Jewish Enemy by Jeffrey Herf if you are interested in further reading. They offer a diverse set of interpretations on the subject of Nazi anti-Semitism. Herf particularly covers the use of propaganda well and emphasizes the impact this had on German public opinion.