See

Oh, Schlitz: How a Historic Ad Campaign Helped Kill America’s Biggest Beer Brand

https://vinepair.com/articles/schlitz-history-ad-campaign

People can write anything for a newspaper, but that doesn't make it true. There is no evidence presented that this advertisement campaign had any meaningful negative imapct on Schlitz's perception, or indeed that it was widely perceived as "drink Schlitz or I'll kill you". It would be very, very strange if it was widely perceived that way, because the advertisement is clearly threatening someone who intends to take away the actor's Schlitz. "Don't take away my Schlitz or I'll kill you" is pretty far removed. Now, you can remark on whether or not that's an effective advertisement, but this seems like a bit of journalistic sensationalism and the brewery's troubles seem more related to engaging in enshittification before it was cool.