Because these are people who are proposing raising INCOME TAX on upper middle class people who work for a living...not that I rtfa, but this is the game that has been played for the past 40 years by these people, so don't expect them to change their tune.
I know reading the fabulous article is passe, but you might want to try it from time to time. For example, had you rtfa you would have noticed that the tax increased don't kick in unless you make more than $655k per year. If that is your idea of an upper middle class income, I would love to have you for an employer. I'd be rich.
But hey, it's not like we can expect you to be informed just because the article is conveniently linked in the header these days.