I really don't understand why they added that risk and thought it was ok. There's already enough tension with him potentially dying from the particle impact. Why bring in a black hole? Why not just have the Wormhole close on its own after a short period of time instead? That way Barry still faces a challenge without endangering everyone else.
I'm willing to overlook that big flaw because everything else about the finale was really well executed but I can understand why that would ruin it for someone.
The finale honestly ruined a lot of the goodwill I had towards the show, because everyone makes the single dumbest decision possible, all to facilitate what Barry wants. Nobody wants it to happen save for Barry and Thawne.
The reason they added the risk is because they needed a consequence of fucking with space-time (which is what happened), but didn't want to affect the entire universe, so they create a single, isolated event that clearly still screws with reality, but no one else has to deal with it.
Essentially, they wanted the character moments, but they also wanted to advance the plot they had planned. The singularity was their best idea, which I support, but having to sacrifice the integrity of the characters in order to accomplish this I feel is idiotic and poor writing.
