Did he look so far down on them that he thought they deserve it?
Or did he not use it?
Edit: grammar
From my own study of the subject I feel the reluctance of Germany to deploy chemical weapons during WW2 had more to do with genuine tactical considerations. Germany had a well matured chemical weapons program by the start of the second world war. They possessed large stockpiles of early generation agents like mustard and phosgene, and had jumped well ahead of other nations in the development of modern chemical agents in 1937, with the discovery of Tabun, the first nerve agent, quickly followed by Sarin and Soman towards the end of the decade. In terms of lethality and effectiveness these agents were a huge improvement on those deployed in the Great War. The German Army had also put a great deal of effort into developing better ways of deploying these chemical agents onto the battlefield, forming what were called Nebeltruppen (smoke troops) units whose cover names employed their battlefield role was deploying smoke screens rather than poisons gases. These units were equipped with the effective and flexible Nebelwerfer rocket launchers and mortars which guaranteed the German army effective deployment of chemical weapons on the battlefield.
However, these troops were never called into there role for good reason. Practical experience from the Great War showed that chemical weapons were not battle winners in themselves and did not guarantee success, as all nations equipped their troops with modern and effective countermeasures to gas attack following the hard won experience ofthe first world war. Secondly, and probably the most importantly Nazi Germany feared retribution in kind. Battlefield use of chemical weapons would open the floodgates for full scale usage by the enemy. The Germans guessed, correctly, that their opposing nations were in the process of developing nerve agents like they had but were not at the point to begin producing large stockpiles for immediate use. Deployment of German chemical nerve weapons would just give the allies the impetus to expand their own production base and would quickly outstrip the German industrial ability to produce and deploy chemical agents. Like the allies, the German army kept large stocks of chemical agents to hand but only fr the purpose of replying to an enemy chemical attack in kind. The risks of deployment were not worth the possible rewards.
It is true that Hitler was gassed during WWI.
Hitler Probably distinguished between gassing in gas chambers and gas attacks, as when you drop a bomb with gas in it. That is probably the main reasoning behind Hitlers logic in your question.
You imply that Hitler chose to gas the jews. In the holocaust reseach field it is not a known fact and historians are still discussing wether it was Hitler himself who planned and commanded the holocaust or if it was the 'nazi system' (as in Nazi officials/ the bureaucracy and so on) who collectively came up with the idea, and Hitler only had a smaller part in this. The historians who argue that the holocaust was Hitlers idea, are called "intentionalists" (as in it was Hitlers intention to do the holocaust). The historians who argue that it was the nazi system who came up with the idea, are called functionalists.
Obviously Hitler hated the jews, you can especially see this in his speeches, but there is no known document where Hitler commands the killing of the jews.
So, the military side of things is covered /u/Mrprocrastinaut below but the process of deciding on gassing victims in the Camps was actually a different one, which I discuss here: