The difference is burden of proof, and the difference is intentional, not absurd.
Because being convicted of a crime is a Very Big Deal, because you are dealing with a person’s liberty (maybe even their life, in the US), criminal charges must be proven beyond a reasonable doubt. Not only must you be pretty darn sure the guy did it, you must be so sure that to doubt the fact of his guilt would be unreasonable. The doubt cannot be “fanciful, imagined, or conjured up to avoid performing an unpleasant task.” (Black’s Law Dictionary, quoting U.S. v. Johnson, 343 F.2d 5.)
For civil cases, OTOH, the burden of proof is preponderance of the evidence, that is, evidence tending to show the fact to be proven is more probable than not. You as a juror may still have some shred of doubt as to whether it really happened – because, really, how can anyone ever know to 100% certainty what really happened if they didn’t see it with their own eyes? – but if the weight and sufficiency of the evidence indicates a particular fact is true, then under the “preponderance of the evidence” standard, you as the juror find that it is true.
Before you decry the differing standards as absurd, which one would you change? Would you have people convicted of crimes on only a preponderance of the evidence? Or would you award plaintiffs damages for wrongful conduct only if they can prove the wrongful conduct beyond a reasonable doubt?
There are very good and solid reasons for having different burdens of proof in criminal and civil matters, and the fact that the burdens are different does not itself make the difference absurd.
Now, if you accuse a man of a crime under the higher standard, and the jury finds him “not guilty,” why should a later civil suit therefore be absurd? Recall that in the U.S. “not guilty” doesn’t mean “innocent” – “We’ve decided he didn’t do it” – it means “not proven” – “We’ve decided the State did not successfully prove its case.” A jury may have very strong private convictions that a defendant is factually guilty (that he did in fact commit the crime), but if the State has not met its burden of removing all reasonable doubt, then the jury must acquit. But because a “not guilty” verdict means “the state didn’t provie its case,” it is not dispositive in a civil case. Why? Because the civil case is concerned with whether it is more likely than not that the guy actually did it, not with whether the State successfully proved he did it. So a “not guilty” verdict in a criminal trial is certainly relevant in a civil suit – the defendant almost always will be able to point out he was charged and acquitted – but it is not dispositive – it does not bar the case.
So the two different burdens of proof are not absurd and, because there ARE two different burdens of proof, allowing both cases is not absurd either.