It seems to me that it is right for any Christian to use discernment regarding tares that might be among the wheat.
The instructions of the parable, though, are to wait for the harvest and let the harvesters separate wheat from tare.
Nonetheless, we are to mark those who do not live as taught by the apostles. Some we are to avoid and some we are to attempt (humbly) to restore.
John has an interesting bit of advice: "they went out from us because they were not of us."
Thank you for your reply, xzins. I appreciate your thoughts on many matters.