You don't need to sell me on Goons. It's one of my favourite cards - probably my second favourite. But it's really not so simple. For any of that second paragraph to be true, you need to be able to consistently have goons in your hand. And so to answer your question about what single card I'd want in my deck, it would probably be familiar, then witch, then mountebank, then possession, and then MAYBE goons (but maybe not... Golem? King's Court? Grand Market? Colony? Vineyards? Chapel? Ambassador? All possibly better. Maybe even wharf).
But the biggest point is that I don't think you understand the point of the Hunting Party deck, which is totally different from a lab-centered deck. The HP deck gets 1+ silver, exactly 1 gold, and 1 (or occasionally like 2) of a terminal silver or terminal-silver equivalent (bridge, or, in this deck, Horse Traders). It then buys a lot of Hunting parties, and sprints through the provinces, being able to reliably hit $8 every turn. Now is it worth it to wait and have Goons be your terminal silver? Well, it depends on what other terminal silvers are on the board.
So the curse-givers are more important, there are some specialized decks (let's not forget quick combos like Native Village/Bridge, some forms of native village/stash), non-province VP sources... it all adds up to around 15-20% of the time you don't want goons (given the opportunity cost). Of course, that still makes Goons one of the best cards in the game, just not unbelievably broken.