Arial Black
Adventurer
So I will try to state this nicely.
First, anyone who starts with the a priori argument that I am "nerfing" players has a certain mindset that is usually not conducive to productive conversations; at least, not with me.
Second, as evidenced by my other posts (including the part that you are omitting; selective quotes to make an argument is often called inaccurate, which is why in any evidentiary proceeding, if a person wishes to read a part of the record, the other side can demand that the full document be entered so that the context isn't lost), if a player demanded this ability*, and the rest of the table was agreeable, I'd just give it to them. If a person wanted to sacrifice rats because they were a Warlock, more power to them- Warlocks can be creepy. If a person wanted to hex all the time, that's fine too. But I'm not a huge fan of retconning bad fiction to justify rules exploits.
Third, D&D is not chess. If you wish to use rules examples, you might imagine the difference between soccer (futbol) and football (American football). Soccer has very few rules; there is no need to have a specific rule for a player shooting another player, for example. Football, on the other hand, is nothing but rules upon rules upon rules. And when someone (Belichick), exploits a rule in a certain fashion, they create even more rules. And more rules about rules. There is nothing wrong about either system, but they are different ways of administering a game.
Given that I have to deal with people that, usually incorrectly, try to exploit rules all the time in my day-to-day job, I prefer not to deal with those that try to do it in my hobby. Others might enjoy it.
*Which wouldn't happen, because that's not the type of table I have.
I better quote you in full, just in case you think I'm trying to twist your words.

You don't like the accusation of 'nerfing'. The trouble is, you are telling me what you rule, and that ruling is a nerf. It is a ruling which goes against the written rules which has the sole effect of taking away from the warlock's abilities, for no better reason than you don't like it.
RPG are strange in that they are simultaneously 'a game with rules' and a shared rule-less storytelling experience. But the rules are part of it. If you change them as DM, you can be fair, or you can be unfair. There is no 'rule' that says you must be fair, but shouldn't we?
If the rules as written lead to a role-playing consequence that you don't like, then go ahead and change it. However, the specific change you make can either make the warlock (in this case) more powerful than before your change, less powerful, or about the same.
The change you are proposing makes the warlock less powerful. This is known colloquially as a 'nerf'.
You could just as easily, and surely more desirably, make a change which does not alter the power level of the class significantly from the way the rules were originally written. In this case, changing the spell so that it doesn't require an initial target solves the 'I hate bag of rats' while also leaving the power level unchanged an leaving the rest of the rules unchanged.
As opposed to changing the way spellcasting works AND