One of the theories is that the vaccine actually trains your immune system to overreact the next time it comes in contact with the Corona virus or a new and deadlier strand of it(the next pandemic) which would cause a lot more damage to you than the virus itself. Strokes, organ failures and so on, coupled with the already overcrowded hospitals and the influx of all the people experiencing these "side effects" would be disastrous.
So maybe that's what's going to happen, but who knows.