I’m not convinced by this, actually!
Like, this analysis treats it as a substance problem, i.e. “edible matter from fairyland has properties that, if ingested, physically prevent you from being able to return to the real world.”
But OTOH, a recurring theme throughout fairy stories is that they’re all about…rules and exchanges and agreements with really steep interest rates:
“I’ll do you this favor, but if you don’t guess my name you’ll have to give me your first-born child.”
“You’re gonna be real good at everything but when you’re 16 you’re gonna prick your finger and die.”
“You loaned me $2 for the bus when I looked like a beggar, so now here’s a literal pile of gold and shit.”
Not to mention that in Childe Rowland, one of the central “if you eat food from fairyland you’re stuck there” stories, Rowland manages to retrieve his siblings despite them all presumably having chowed down on fairy food – all it took was beating the Fairy King in a swordfight and threatening to chop his head off.
The takeaway, I think, is that the food thing a matter of implicit exchange: if you get your grub on in fairyland, you’re accepting their hospitality and eating food that they own. This means you owe them, which the fairies can magically leverage to prevent you from leaving.
(You can probably get around this by explicitly agreeing to pay for your meal before you sit down to eat. From what I remember, fairies don’t seem capable of pulling a “Haha, we had an agreement but you’re fucked anyways!” maneuver, so if they agree to let you leave they might even be forced to help you leave.)
Which brings us to the matter at hand: if you blow a fairy you’re doing them a favor! They owe you.
And…they’re a fairy, so if you didn’t agree to terms beforehand they might not repay you in a way that’s ultimately helpful or safe, but it certainly doesn’t seem like they’d be able to, like, pat you on the head and be like “Thanks, you’re really good at this buuuuuuut also you’re stuck here forever now.”
Instead, what seems more likely is…I dunno, showing up to your wedding years later and giving you a beautiful white horse that always comes when called, while loudly praising you as truly deserving it for giving them them simply the best oral they’ve had in years.