I was pondering this myself for the past few weeks.
I have come across so many Believers who do not have the fundamental Truth OR those who have twisted just enough to deny the Truth and then our local Cardinal wrote an opinion column in our Secular Sydney Newspaper that Islam, Jews and Christians all believe in the same God (I even posted here for anyone who wanted to have a read of the heresy being peddled).
We must be coming so close to the Tribulation starting because an attack on God's Truth and people falling away in droves (following these lies) are certainly signs pointing to the Day of God's Wrath.
You can do nothing for those who refuse to receive God's Truth. I have tried time and again to point people on other forums to consider God's Word. I never push I just say consider what it says here and try to give some simple interpretation if needed and supply some extra supporting scriptures. There are some obstinate minds and hearts out there.
In the end I have decided to withdraw for a while and praying for those who are adamant of destroying themselves and taking others with them.