That is absolutely horrible UX: User interaction should not be required for your site to be legible. If you are one of the 0.000001% of people who wants all line breaks to vanish configure reader view yourself and hit that button, but don’t force 99.999999% of users to make that extra click.
Counterargument: if you need narrower text, you can adjust the size of your browser window. If I want wider text, you’ve capped it.
That is absolutely horrible UX: User interaction should not be required for your site to be legible. If you are one of the 0.000001% of people who wants all line breaks to vanish configure reader view yourself and hit that button, but don’t force 99.999999% of users to make that extra click.