Why must yefas toar be allowed
We have in Ki Setze the laws of 'yefas toar' meaning a non-Jewish woman captured in war whom a Jewish man now wants as his wife. The meforshim (commentators) say that the only reason this was allowed is that if there were a law against it it would not be kept since the yetser hora (temptation) is very strong on this. So rather than have people sin, Hashem made the law that it is allowed.
Why must Hashem gave allowed it? He could made the yetser hora less on this and then people wouldn't sin.