One flaw in the lensrental essay about protective filters is the estimated cost of replacing a front element. I believe the author says about $150, which might in fact be his cost if he is ordering the part and doing the labor himself.
However, even for Canon Professional Services members, you'd have to add about $150 for labor, and then the price of shipping the lens (insured!) to Canon, which costs about $70.
And, of course, even with rush service, you don't have your lens for a week.
I'd rather clean the filter than the front element. A filter already saved my older 24-70mm in a tripod mishap some years ago.
As for image degradation, I've taken many test shots to compare side by side, as some experienced photographers have expressed concern about it. I see no loss of image quality with B+W and better Hoya filters--not even star effects in night shots. If I'm concerned about flare, I can pop off the filter briefly.
To me, the biggest peace of mind comes from being able to clean the filter. So easy in the field to get muck splashed on it, or a stem hitting it while walking through brush. In that tripod incident, the ef 24-70mm fell forward onto a small stone (no, I don't blame my wife, I should have explained the basics of the tripod!). The Hoya filter smashed, but I didn't get a scratch on my front element.
And as has been said: Canon advises using the filters on L lenses to complete weather sealing. If my car manufacturer recommends specific tires, fluids, etc, I take the suggestion seriously.
I remember when people would swear seatbelts cause more harm than good.