Nice graph. No sarcasm - it is interesting.
A lot of taxes only come in place when you hire someone. For example, making employers pay for health care. I'm not saying that the employees don't "deserve" health care or even really touching on that - but if I was an evil rich businessman, when you put a new tax like that... I would just lay people off. If I was rich and evil. You can't outlaw greed, and when you kinda sorta try to - you get unintended consequences.
Now if I was a more middle class guy trying to open up a pizza place, I would need employees. But with these types of taxes I couldn't afford to hire as many. So I wouldn't. That lowers employment. But even past that, with fewer employees, my business may fail, and that KILLS the economy. (not only must I hire less people, but now I can hire no one.)
With any tax, you are not really taxing the buyer or the seller. You are taxing the transaction itself. In this case, you are taxing employment, NOT the employer, but both employer and employee. It is often framed in a way that is supposed to protect the poor and middle class from the rich, but from my view the true effect and purpose of these taxes is to prevent the poor and middle class from rising.