Not a downvoter, but this theory gets tossed around in bars and over dinner in LA sometimes (LA was one of several cities where this scenario played out).

Short summary, it's not clear, in LA at least, if the GM/Goodyear "intentional destruction" scenario really did the Red Line in. The ridership had been decreasing for several years before the purchase of the Red Line. Long-time residents say predictable things -- autos were more convenient and faster than streetcars.

Short of doing your thesis on this, it will be hard to separate the truth from the legend on this story.

(Not a public transit hater.)