There is an irrational, knee-jerk reaction to the phrase: "Bag of Rats".
In reality, the laws of physics work how they work. What you or I think about those laws can not change how they actually work.
In our D&D fantasy worlds, spells work how they work. Spells do exactly what it says on the tin what their description says they do. The opinions of how the creatures in the game think spells should work have no bearing on how they actually work.
Similarly, the opinions of the players of the game do not alter how spells work in the game....on a whim. A DM/player may make houserules, but that effectively changes the spell description,sure, but it cannot be that a player's/DM's opinion on a creature's motive for casting a spell changes the spell description, i.e. change how it actually works.
The hex spell works how it works. If you change the spell description as a houserule, then it works how its revised description says it works.
But it cannot be that the spell works as it says it does....unless the DM doesn't like your motives for casting it on that particular valid target because they don't like your perceived motive.
Player: I push over this crumbling wall onto the bad guy so that the falling bricks kill him.
DM: Great idea! The bad guy takes....rolls... 15 damage and dies.
Player: I push over this other crumbling wall onto the cute but helpless puppy, just like I did before with the bad guy.
DM: No. Bricks don't work that way. I don't like your motives so the laws of physics stop working. Bag of Rats.
It's well known that using spells according to the rules is an 'exploit'.
Bollocks.
Usually, while camping, I go to sleep at night, wake up in the morning, and then cook breakfast. If my party had live chickens with us for the purpose of us eating fresh food instead of food that goes off, then I kill a chicken and cook it each morning, and use the meat for breakfast and to prepare cold sandwiches for short rests throughout the day, along with other food.
If I'm the warlock, what's stopping me hexing the chicken the moment before I kill it? What law of physics or magic prevents the spell from working in a manner consistent with the spell description?
The meta-"DM doesn't like it" law? Ah, so the value judgements of the players of the game can actually change the laws of physics/magic in the game world? Right, I don't like the motives of the BBEG, therefore his disintegrate doesn't work on me! See? It clearly states on my character sheet that I am as cute as a puppy!
Do you play chess? I'm firmly of the opinion that your queen's motives for checkmating my king is an 'exploit'! Therefore you did not checkmate me.