Well, let us just agree to disagree. 1John1:5 is scientifically discernable as an addition, besides why did not the early Church Fathers bother to use it as source material when they were discussing the Trinity during the Nicean era?
If being a trinitarian is necessary to being a Christian, what about the other famous fractures -- like monophysitism or Revelations (the Ethiopeans do not consider it part of canon, the Armenians rcommend you do not believe it, no Orthodox Church uses it in Litergy). Do these beleifs (which go back much further than your or my Protestantism) make them "Sects" or "cults"?
It is possible to consider Father, Son, and Holy Spirit as three separate divine entities or aspects of one entity whgich is greater than any of the three and still believe in the literal diety of Christ Jesus. These may be different than your beliefs but I (and most of the world) do not believe either against him or his teachings.
P.S. the vast majority of Quakers are trinitarians, we are not very exclusionist, so unitarians, universalists, Buddhists, Jews, atheists, and pagans all are welcome (at least to most Meetings).
If you wish to consider these groups along with Unitarians, Universalists, and Quakers as "sects" or "cults" that is an abuse of either term. If you believe that non-Trinitarians and Monophysmatics and the Armenian Church and the Ethiopean Church and the Coptic Church all "against him and Christian teachings", I suggest you pay attention to the plank in your eye before you point out the mote in ours.
Pax et amor vincunt omnia, radarmark