Of course I think it is fine, but I believe very strongly that it should be done in the basis of relationship and trust, and in the context of a positive teaching and discipling ministry.
What I think is absolutely out of order is the ministries that think that their sole or even main purpose is to call out others. Not Biblical, not in the slightest.
So for example, we have a couple of people in our church who have just been to see a certain charismatic minister. Now I know that her whole ministry is based on falsehoods and deceptions, so I have told them that and showed them from the Scripture where her ministry is wrong. They thought there was something wrong in the meetings, but could not put their finger on it.
But I don't start a blog against her and follow her every move around the country. I didn't go to the meetings with a placard and call her out. Too busy preaching the gospel, teaching the kingdom and healing the sick to do that. Anyone who does just that is not following the commands of Jesus, they just do not have the time. And it is no-ones primary calling, look at Ephesians 4 and see what the primary functions are.
In addition a lot of these watchdog ministries have no discernment at all, you find them at Copeland meetings, Andrew Wommack meetings and many meetings of great preachers who base what they say on God's Word. It shows how little you can trust them.
I say: feed the sheep, let them grow up and a lot of these issues disappear. Walk in the Word of God, teach the positive and people will recognise the negative.
A lot of the calling out stuff that goes on has a real nasty tone to it, as witnessed by the Todd Bentley stuff. Would I go to Todd Bentley if he came to town, no. Not to get bammed, not to criticize, I would just keep doing what I am doing - helping Jesus build His church.