I very highly doubt they were drunk; it's illogical and there's no evidence to support it. No reputable source would even posit it. That doesn't mean they didn't drink, but there's a difference between drinking and getting drunk. That's an interesting theory about the British aristocracy, by the way, but it looks to me like one of those trends that people notice in hindsight, rather than a conscious decision on the British aristos' part.

It was a terrible series, from the point of view of historical accuracy--and yet so much better than some! I posted a detailed commentary on it a couple of days ago. You would really have had to see the context in which Robespierre was taking the laudanum... It really didn't look like it was for medecinal purposes.
I can see how a laudanum addiction might be thought of as a vice, even in the 18th century, just from the standpoint of overindulging in general's having long been viewed as a vice.