No, those that are not Creedal professing Christians are not allowed to post in the Christian area. They are not Christians. They may read, but not share their atheism or heresies among the body of Christ.
Mat. 7-15, "Beware of false prophets, who come to you in sheep clothing, but inwardly are ravenous wolves."
We are warned not to allow them to proselytize us
2 John 10-11 If anyone comes to you and does not bring this teaching, do not take him into your house or welcome him. Anyone who welcomes him shares in his wicked work.
Jesus , Paul , and the disciples did not believe that meant allowing them to teach you , and then you thank them
Those that refuse to hear and that instead try to teach you , have not heard. What did Jesus say?
Mar 6:11 And whosoever shall not receive you, nor hear you, when ye depart thence, shake off the dust under your feet for a testimony against them. Verily I say unto you, It shall be more tolerable for Sodom and Gomorrha in the day of judgment, than for that city.
I truly understanding the doctrine of separation. We have an Amish community here that is the very embodiment of that doctrine. And I understand the Scriptural basis for doing it.
But taken to mean more than Spiritual separation, one could become a modern day Pharisee and thus run contrary to the Great Commission and also to the example set by Jesus: