I was once agnostic as a teenager. Agnostic means not being sure, searching. John never said he was an antichrist. None of the apostles ever said that they were antichrists at one time. No preacher stands in the pulpit delivering a sermon on salvation every calls the unsaved in the pews as being antichrists.You rejected Jesus also.
"antichrist" has an especially negative cognition to it.
Being an antichrist requires that a person be a Christian, who falls away and denies Jesus. Such persons are in Hebrews 6:4-6.
4 For it is impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost,
5 And have tasted the good word of God, and the powers of the world to come,
6 If they shall fall away, to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put him to an open shame.