Using the 1920 manifesto as "proof" that the Nazis were left-wing is completely absurd. The Nazis under Hitler were not left-wing, nor where they ever considered left-wing by the people of that era. The Manifesto had nothing to do with what they did later on. You might as well use young JFKs opinion that "fascism is doing great things for Germany/Italy" as core beliefs of his later political career, it would be completely nonsensical.
The whole point of the name of the party was to appeal to everyone. The working-class wasn't dead-set on being communist at that point, but it was definately leaning towards that direction. As such, the Nazis tried to appeal to them and lure them away from the KPD, hence the word socialist. At no point did the Nazis ever try to actually be socialistic.
What the Nazis actually did, was cover all bases. They promised everyone exactly what they wanted to hear. To achieve that, you obviously couldn't have a certain set of ideals, on the contrary, you had to keep your plans as vague as possible. Which is exactly what the Nazis did.
They promised the farmers higher prices, the industry help against the unions, the workers job-security and higher wages, the old military class a bigger army and the nationalists a new German Empire. Which makes it blindingly obvious to anyone who does bother to think, that they were quite clearly not socialists. Instead they were a whole bunch of things, in many cases even holding contradicting views. They claimed to be exactly what each "class" wanted them to be. All of that was just an attempt to seize power. It was completely impossible to uphold all the things they promised, as they made promises to opposing sides.
It doesn't really help civman's point, that the only people you could in some way describe as the left-wing of the party (the Strasser brothers) ended up being "removed". Not that they were what civman claims either. Gregor Strasser himself was pretty close to the industry and dropped any stance that went against their wishes even before he lost power in the party.
And no, you cannot just take the name "national socialist" and then remove part of it, declaring them to be socialists. That's not how it works. As pointed out above, the Nazis always told the audience exactly what it wanted to hear. The workers got promises that increased their rights. Just like the industry got promises that they would get rid of the unions, make it easier to exploit workers, and even gave them tax-breaks.
As for picking a random Hitler-quote and using it as "absolute proof" for your argument, just take a look at his peace-speech from May 1935. You couldn't get more pacifist than that, yet he was happily planning his wars of the future at that time.
Just a few bits and pieces:
What dynastic egoism, political passions and patriotic delusions achieved by shedding oceans of blood has, after all, only scratched the surface of peoples. How much better results would have been achieved if the nations had applied a fraction of their sacrifices to more useful purposes? Every war means a drain of the best elements. Victory can only mean a numerical addition to the victor nation’s population; how much better if the increase of population could be brought about the natural means, a national will be produce children of its own!
The national socialist Germany wants peace out of its utmost ideological convictions. Furthermore it wants peace out of the primitive awareness that no war would be able to deal with the plight of the people of Europe, it could only enhance it.
What else could I wish for other than peace and calmness?
If someone says that this is merely the wish of the leadership, I have to give the following answer: if only the leaders and rulers wanted peace, the peoples themselves have never wanted it! Germany needs peace and it wants peace!
I guess that settles it, WW2 never happened! How could it, Hitler himself said that he wanted peace
But clearly the Nazis were left-wing. That's why they got rid of any leftish bits of their own party, banned the communists, hunted down social-democrats and wiped out the unions
