First of all, anyone with just a slightly open mind, can see there are quite a few Scriptures to support eternal punishment, annihilation, or the salvation of all mankind through Jesus Christ. Throughout the centuries there have been sincere Christians in all these groups. You see, apart from the spirit of revelation, which comes from above and not from ourselves, the Bible can really be made to say anything we want it to say. Look at the thousands of denominations each based upon differences of interpretation of basically the same Bible. Most Christian cults are even more intense in Bible study than average church-goers and they often come up with some very bizarre teachings.
Most people are usually sincere in their beliefs.
They really believe they have the truth. The Scriptures, apart from the spirit of revelation often produces horrible systems of belief. Few of us are honest enough with ourselves to cry out to God to be completely set free from the traditions of men, from cultural, parental, political mind-sets which effect how we read the Scriptures. The teaching of eternal torment has permeated the Western civilization for about 1500 years. Few realize the early believers were not indoctrinated into this mind-set by Christian leaders.