As of April 30, 2020, the Mercedes Alabama plant employed over 4,000 people. That only brushes the surface of what having a plant like that in the area does for the positive. There are thousands if not tens of thousands of other people, in the immediate area, who make income from that plant. Machine shops, mold shops, transportation, food and hotel, etc.. You are being extraordinarily short sighted if you think that plant doesn't benefit the local economy immensely. I've seen very close up the devastation left when a large automotive plant closes the doors. Ask Muncie, Anderson and New Castle Indiana if they'd like their automotive plants back.
While the company itself may get many tax incentives and freebies, how about the income taxes on those 4,200 employees? If the average income is $40,000, that generates $168M in taxable income. At a 30% tax rate, that's over $50M in Federal taxes created. When you add in all the other jobs created in the area, well over $100M in Federal taxes are paid. And even with Alabama's low State Income Tax, at even 3% on average, over $5M in State Income taxes are paid.
Most automotive companies also provide fairly reasonable health insurance benefits. Where are all those people going to find comparable jobs with health insurance benefits near Birmingham?
Automation does not eliminate all jobs. You been watching too many Terminator movies. It does indeed decrease the number of manual labor jobs which would be, of course, lower in pay. However, it creates many more technical jobs for people to operate and maintain the machines.