If there is anything I've ever seen that is heretical, it is what you just said. There is a basis and that is the problem. Christians actually believe God's word and accept it. Philosophers playing at religion don't believe God's word and resort to their moral and intellectually relative judgements of what might be best given their relative understanding of the notion of being "good" vs being "evil".
For the Christian, it is understood that we are not allowed to stand in God's reserved place of mortal judgement over another person due to that person's sin. We can call it sin - recognize it and refuse to participate in it; but, the moment we stand in God's shoes and usurp His role, we are in sin and guilty of the blood we spill and of the soul we may send to hell in the doing. There is not only a basis but an absolute basis and what you said is indicative of the problem.
Doesn't one have to be a believer in order to be a heretic?
So you don't think you should stand in judgement over your fellow humans, eh? Doesn't it give you pause that others Christians who believe just as passionately as you, and maybe more, have a different conclusion? It's historical fact that standards and beliefs have changed dramatically over time and from place to place. To me that is powerful evidence that absolute values, should they exist, are unknowable by us.