The Chilling Effect was thoroughly covered in my Constitutional Law class during my year in law school. I understand that this is what any argument for First Amendment protection of E2E would ultimately rely on, but you generally have to actually need to measure or "plainly observe" said effect. Since most people couldn't tell you the difference between end to end encryption and encryption in transit (I can only sort of do it myself), it's really difficult to argue that restricting E2E encryption would actually have a chilling effect.