Let's start with "#TheLeft" because thats the easy part.
It's called so for the seating order of the post-revolutionary parliament in France [ the ol headchoppers ]. As opposed to "#TheRight" which was (obviously) sitting on the other side.
As you can see, even the name doesn't make any sense but, like with so many other historical stuff, you can't get rid of that.
One cool thing about being part of the left is, that you have the inbuildt superpower of the moral high ground.
Above critique.