Well actually he's quoting the judge father of the woman interrogating him. But still a great line :)

Well actually that attribution is purely fictional. In reality the quote is properly attributed to Picard because Picard is the first fictional character to actually say the quote.

I'm not convinced that a "direct" quote from a fictional character bears any more weight in reality than a fictional attribution to another fictional character. Shouldn't the quote be attributed to the show writer(s)?

It is a silly distinction, but: In reality, millions of real people have observed Picard uttering that quote while zero real people have observed the judge's father uttering that quote.

If we're making silly distinctions, in reality those people saw Patrick Stewart utter the quote.

I would argue that it is not remotely silly to make a distinction between phrases uttered by an individual and phrases uttered by an individual playing a character (especially with pre-written lines). I would be far more comfortable attributing the quote to the writers of that episode than to Patrick Stewart.

However, in practice, it is difficult to attribute specific lines to specific writers given how scripts are produced. As such, lines are generally attributed to the characters that speak them.