First of all, people, in England, turned out to watch hangings, beheadings, and such ( don't forget the whole people in stocks...there, in Bermuda, and in Colonial America...in later eras ) for several different reasons. One was to teach their children to NOT commit crimes, another was to see the guilty get what was coming to them, and some, probably just took some kind of pleasure from viewing these acts.
Secondly, such viewings went one hundreds of years PRIOR to the 1700s, as well.
Now...as far as pick pockets go...child pickpocket gangs weren't anything "new" when Dickens wrote OLIVER TWIST. Pickpockets of EVERY era, gin or no gin, went where the people congregated. There are even extant records of pickpockets roaming through the crowds, who massed to watch PASSION PLAYS, at Easter time, in the Middle Ages.
But you ARE on the right track.
Fascinating...but what would they pick out of the pockets? Practically no one had money at the time, it was one of the reasons the Templars became the traveler's cheque technology for those who were crusading and/or pilgrimageing.