The film starts out in the hallway of a German University in front of a bulletin board. With the exception that the language was German, from the clothing and demeanor of the two students, a young man and woman, you could've mistaken it as a scene from an American University in the 1930s.
The topic of a lecture came up regarding the euthanization of the mentally defective and the man suggested that they attend the lecture. The woman on the otherhand says, "I was taught that euthanasia is always wrong." The man rejoined with "maybe we should be open minded about this and attend anyway." The woman agreed.
The next scene shows the students attending the lecture and I must say I found myself in agreement with the lecturer, he made perfect sense. All his psychological, sociological and economic arguments made perfect sense.
I also knew that the Germans began their program of genocide by initially liquidating the mentally defective and also knew that no matter the reasonableness of the lecturer's argument he was wrong and what he was proposing was equally wrong.
Some respond, when one mentions a "slippery slope", that one's just blowing things out of proportion. This film wasn't just evidence that there is a "slippery slope" but that it's also quite easy and rational to end up on one.