Pennywise kills a handful of people every 27 years and has been doing so for 300 years or so. He probably has kill count under 100.
Between the kills he gets that are directly shown on screen and the number of casualties you could reasonably assume were the result of his actions, Heath Ledger’s Joker probably killed a few thousand people.
Ronald McDonald on the other hand, was the main marketing vehicle for a company that sells food products that are incredibly unhealthy and addictive. He is probably indirectly responsible for the deaths of millions of people.
Heart disease kills several orders of magnitude more people than extradimensional demons or psychopathic clowns.
Heart disease kills several orders of magnitude more people than extradimensional demons or psychopathic clowns.
And if you factor in politicians, you have psychopatic clowns killing millions by passing policy that objectively helps keep those heart disease numbers up!
It's a well known fact that advertising never works and is a waste of money. That's why the entire industry died 80 years ago, and nobody ever published an ad ever again.
Considering Ronald McDonald was a character primarily aimed at young children, I don't think they were mentally capable of having personal responsibility at that age.
As for the parents who were pestered to buy happy meals by their children, there's like 50 ways to answer this question. I personally think that in a mentally healthy adult, personal responsibility is a factor, but it's not the only one and is balanced by social conditioning, genetic predispositions, mood in the moment, and a ton more factors.
The children who for one reason or another were brought up eating fast food are conditioned both socially and biologically to eat fast food, and breaking out of that addiction (as with any other addiction) can be very difficult, and is more complex than doing the equivalent of saying "git gud scrub".
Wow, that turned into a wall of text, sorry.
Tl;dr: it's way more complex than just "personal responsibility".