Richard Mouw offers some wise perspective for an "evangelical" way of treating those whom we think get it wrong.
"We want to oppose false teachers because they do not teach things that are true. But if in our attempts to defeat them we play fast and loose with the truth, by attributing to them things that they don’t in fact teach and if we don’t really care whether we have it exactly right or not then we have become false teachers: teachers of untruths!
I suggest this as a rule of thumb: focus on false teachings rather than on false teachers. When we concentrate on opposing false teachers we tend to think about defeating people which can lead to all kinds of dangers. When we concentrate on the careful examination of false teachings we are more aware of the need to speak truthfully.