But for the general public that reads such general articles (rather than the FT audience which you were adressing and until now 61 posts and several days into the thread),that you do not cite, redeeming any miles for any ticket, most often Y tickets IS considered a good deal, as the vast majority of those redeemed by US fliers (for example) are for domestic tickets, so again, whatever "common fallacy" you refer to is moot.

As for common FT knowledge, you have not caught me out with any caveats, an emergency is an emergency and even a blind squirrel knows that a same day flight on a packed plane will be expensive even for the shortest of short haul domestic flights and in those cases using miles is a prudent investment.

Again, your preamble and general statement are based on a fallacy which it seems that only you have created. You do know that this place has millions of posts, many of which deal with exactly what the best deals and use of FF miles are, don't you?