First off, 100+ is clearly an exaggeration. And I'd be surprised, but visibly reacting would be rude.
Secondly, I highly doubt they treat you like that for 'having reasonable points.' The way you've written this makes it clear that the way you present your points is what makes them treat you like that.
I also have a last name that is very long and tends not to fit completely on forms. It's never been an issue.
I think
Kirke makes a good point. I also have several friends, and many acquaintances, with 10+ letter long names that have never mentioned it as an issue (Alexandrias, Bernadettes, Cristophers, Evangelines, Gwendolines, Jacquelines, and Wilhelminas just to name a few). A good rule to go by is: If it's not enough of an issue for them to mention, then it isn't a big enough issue that you should mention it.