While the conclusion made in this episode is indeed a logical one, I wouldn't have used the Prime Directive as the absolute reason why the Enterprise shouldn't have involved themselves anymore than they did. I would have just used common sense. We helped you with your ship and cargo, but we will not tolerate being deceived into helping you with your drug business. Simple and reasonable.
I also don't like how Picard's reasoning basically amounts to "You'll have to take my word for it.".
Picard: "History has proved again and again that whenever mankind interferes with a less developed civilization, no matter how well intentioned that interference may be, the results are invariably disastrous."
Example please..... I'm willing to put up with one of your history lessons if it relates to our current situation..... You seem to be dead set on this point Picard.... No, I'm not going to just take your word for it. You violated the Prime Directive once already in this season and the only disaster that came from that was the perfectly good opportunity to legally kill Wesley.