In Christendom there are groups who find themselves exclusive, believing they are the holders of the absolute truth, while all others are heretics or even the work of the devil himself.
From those preaching the Gospel and Baptism in Jesus name
Always there have been real followers of Jesus who only worshipped his One God, the God of Israel. Many centuries they worked and preached behind closed doors, avoiding persecution and death on the balefire. In fear of the stake for centuries the real followers of God baptised people in their faith, not demanding to be part of one or another church but being part of the Body of Christ.
Those willing to tarnish
In the history of Christendom we see many churches which started of as so called cults or so called heretic movements, though many years later they sometimes outgrew their original group and/or became one of the many main churches. Therefore one should be very careful by damning a group or calling ti a cult or sect, when there is not really anything what qualifies it to become called a sect or cult.