You're gonna be surprised to find out United isn't the worst airline out there. In fact, it's not even top-2, and that top-2 is filled by both major airlines in another country.
Your satisfaction and safety is better than it could be!
Even with their recent problems, if you are driving any significant distance to the airport, you're far more likely to be killed in a traffic accident on the way there than you are on the airplane.
They have thousands of flights a day. You have nothing to be worried about. Not that it couldn't happen, but it's so beyond unlikely, it's not actually worth a minute of fretting over.
I think what you mean to say is that a decade ago and earlier it was very unlikely but in recent years it's becoming far more likely, and you should absolutely consider the possibility that the airplane will fall apart because there's no reliable quality control and the company that manufactured it is staffed by amateurs.