I don't really know the exact belief in Satanism. but I suppose they see the will of God upon earth as tyranny, whereas satanism would extend freedom. God speaks of seven sins, seven human emotions like wrath, greed, vanity etc. so, to be satanists is to indulge in them, in other words to be free and human.

I may be wrong though.
so satan is this selfish all consuming side of humanity with all the sins where Jesus is all about the sacrifices and giving. being selfless. Christanity and its Ideals are mindblowing in a sense.
I could be wrong though.