If you do that you should allow 2x strength for people wielding a 2 handed weapon. Otherwise you have 2 shortswords doing 1d6+ Str each vs a greatsword with 2d6 +Str 1.5(notice they 2 handed user only gets 1.5 str much like the current 2 weapon fighter). Now lets look at other things you can do. A TWF can get AC bonuses with feats (TWo Weapon Defense) A 2 handed fighter cannot. As a TWF gains levels and takes feats they get additional off hand attacks potentially. Adding full strength and no penalties would make it idiotic for anybody not to be a TWF