Literally, yes. There must be a hard-coded rule in order for the mechanics to accurately reflect the fiction I want (that of the Paladin's traditional 'fall' mechanic). It the system doesn't provide for that, then it fails to give the fiction I want.
Now, of course it causes problems for many groups; thus my "keep alignment optional" stance, even if I wouldn't play D&D without it. However, I'm still a big supporter of a Paladin being able to fall (and him being only Lawful Good, in the alignment option).
I would be okay with other options being presented, though. Not even "alternative" options; just other options.
Well, of course, my players want things to work however I tell them the campaign details are (low magic, gritty, low population, spellcasters distrusted / revered, etc.), with very, very few exceptions; but, they really trust me as the GM, and have expressed that I have a greater vision when it comes to what will make for running an interesting campaign than they do (but I have so much more practice, as a lifelong RPG GM).
But, your solution is "if you want the traditional D&D Paladin 'fall' mechanic, then houserule"? Now,
that I consider silly. But that's just me. As always, play what you like