God is unjust again

Deuteronomy 19:15 says, "One witness shall not rise up against a man for any iniquity, or for any sin, in any sin that he sinneth: at the mouth of two witnesses, or at the mouth of three witnesses, shall the matter be established." So, once again the wisdom of gods words sounds once again for the transversely of crime. This verse is saying that if you are going to commit a crime. Make sure only one person can witness it. Rape would be a good one. There is typically only one witness and that is the victim. Then again, the way a woman are treated in the bible( like cattle), rape is probably ok. I mean, if you look at the wording of this verse witnesses are onlymen. So women should try to avoid having crimes comitted against them. But getting back to the main issue, shouldn't one witness be enough? I mean for a caring just god, why would he need two witnesses?