Drug paraphernalia has a specific use (or at least, let's assume that for the sake of argument), but youtube-dl is more like a crowbar that has legal and illegal uses.
If I have a crowbar I can legally use it all day long for construction purposes. As soon as I'm caught breaking into a house with a crowbar, it's classified as burglar's tools. At no point is the hardware store or crowbar manufacturer liable for a burglary for selling me a crowbar.
I don't know what the laws are on possession, but before marijuana was legalized it was far, far easier to buy a bong than the weed to smoke in it. I'm wracking my brain to try to think of a piece of drug paraphernalia that is illegal to sell or illegal to possess in the absence of the drugs themselves.
In the state I live in it's illegal to to be in possession of any paraphernalia. Thats why you cant buy a bong anywhere, but can buy a water pipe at every corner store headshop.
That being said it's a petty misdemeanor that does not result in any jail time until your third infraction.
If I have a crowbar I can legally use it all day long for construction purposes. As soon as I'm caught breaking into a house with a crowbar, it's classified as burglar's tools. At no point is the hardware store or crowbar manufacturer liable for a burglary for selling me a crowbar.