We can be the judges of deceptive teaching using the Bible as our authority - NOT our own authority.
I am talking here of "false gospels". If someone claims EVERYONE goes to heaven regardless of what they believe, this IS a false gospel! What would be the point of Jesus Christ coming to earth, enduring unimaginable suffering on our behalf and telling us we need to go through HIM for salvation if it didn't matter at all in the end what we believe?!
When something is NOT clear in Scripture, we are at liberty to have our own views. I really believe that this is often abused though. For example, is it very difficult to make a case for universalism from Bible texts without blatantly ignoring the huge majority of texts on this issue and taking other totally out of context. If someone inside the church claims everyone is going to heaven (if in fact it turns out they are not), can you imagine how serious the repercussions of that error are?! Surely, its not good enough as simply say its OK to have different views on this - they could be leading many people to hell! Is it really "loving" to describe this as a side issue when the consequences of getting it wrong are so high and Jesus statements on this issue are so clear?