I agree, that statement "God doesn't write the same thing on everybody's heart" clearly is a doctrine of devils and NOT New Testament teaching.
Paul, the apostel to the gentiles told us there are and remain absolutes in the New Covenant, valid for every believer:
Romans 13:9 For this, Thou shalt not commit adultery, Thou shalt not kill, Thou shalt not steal, Thou shalt not bear false witness, Thou shalt not covet; and if there be any other commandment, it is briefly comprehended in this saying, namely, Thou shalt love thy neighbour as thyself.
Ephesians 6:1 Children, obey your parents in the Lord: for this is right. Honour thy father and mother; (which is the first commandment with promise
That it may be well with thee, and thou mayest live long on the earth.
1 Corinthians 6:10 Nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners, shall inherit the kingdom of God.
Galatians 5:21 Envyings, murders, drunkenness, revellings, and such like: of the which I tell you before, as I have also told you in time past, that they which do such things shall not inherit the kingdom of God.