I would say that prevention of a future crime by a perp is NEVER "beside the point".
Circumstantial evidence is all that exists in many cases, and the way that it is debated, usually emotionally, is the difference between a conviction and an acquittal. There was DNA evidence in the OJ trial, and that was presented poorly by the prosecution, dishonestly rebuked by the defense, and not given adequate credence by the jury.
I did not follow every word of the trial as the jury did, but it certainly looked to me like OJ was guilty.