Since no one has explicitly come out and said exactly what the issue is here, I'll ask:
*What exactly is harmful about an opt-in filter? *If it's opt-in, then you have the choice to not even enable it if you so choose. You don't have to use it; it'd just be an option in the preferences page or maybe even a link on the margin similar to the WikiBooks link I never use. Can another option or link you never click really hurt the world, or even an individual for that matter?
You don't get to grind someone's nose into your shit.
Fred