If the argument towards this question is overwhelming, surely someone has made a lecture on it somewhere.
I think it might be because people are confusing asking questions with being against something. I am neither against vaccines nor mRNA vaccines particularly. I just genuinely want to learn the details. I think it is important to know upsides and downsides of each vaccine out there since there are several alternatives.
The mRNA is delivered, causes cells to express proteins and is naturally broken down (it's normal for the body to sweep up mRNAs over time).
Once the mRNA is gone, the long term effect is the immunity, which there's no reason to expect it to be different than immunity to similar antigens, which is something that is well studied.
So the immunity side of it is not a radical departure (antigens are presented to the body) and the delivery/mechanism is quite clear and has a natural brake (mRNA degradation).