Audiophiles who do this do one of two things. They buy a sub and set it to have as low a cut off frequency as possible, which is a HUGE waste, or try to blend them in without high passing the mains. In neither case the results are mediocre to non existent.
Your comment should be clarified to say that this applies to bandwidth limited monitors. I have speakers with folded horn bass drivers. This bass is some of the best that can be had. It would be foolish to high pass LaScalas. So I do just what you advocate against, bring the subs in very low. And it works fabulously.
Not a one size fits all solution, neither is yours.
BTW, I think you meant “either” , not “neither”.