Considering my native tongue is Dutch and I used to live pretty close to Germany, I have some understanding of the German language.
You quoted a text by Brita Schirmer, not by Hans Asperger. In the quotes she produces, I find no indication whatsover that Asperger feared his subjects might be euthanised.
The most relevant quote is this one :
»Wieviel können wir für diese Menschen leisten? soll die Frage sein. Und wenn wir mit all unserer Hingabe ihnen helfen, so tun wir damit auch unserem Volk den besten Dienst; nicht nur dadurch, daß wir verhindern, daß jene durch ihre dissozialen und kriminellen Taten die Volksgemeinschaft belasten, sondern auch dadurch, daß wir zu erreichen suchen, daß sie als arbeitende Menschen ihren Platz in dem lebendigen Organismus des Volkes ausfüllen.«
I wound translate them in modern English like this :
” The question will be : how much can we do for these people? [The answer to this question is obvious, though.] When we help them with all our devotion, we also help our people. We do this not only by preventing them from damaging the community by means of antisocial or criminal acts, but also by making sure that these people find their place as working men and women within the Organic community that is the German people. "
These words are entirely in line with the national-socialist way of thinking and could just as well have been spoken by Hitler or any other national-socialist official. This indicates that either Asperger was a national-socialist himself or that he had a more than superficial understanding of it.