Wrong. It's mentioned specifically twice (Mar 3 and Matthew 12)but alluded to numerous times. You cannot use scriptural scissors and clip out what you don't like or that which discomforts you. We condemn ourselves by our words. Isn't that why it is said:
36But I tell you that everyone will have to give account on the day of judgment
for every empty word they have spoken.37For by your words you will be acquitted, and by your words you will be condemned.”Matthew 12: 36-37
Do not think you may freely say this or that by Free Will, and that GOD who is Ultimate Reality will let it slide. If we ask forgiveness in all but one thing, we can be forgiven (under very specific circumstances). But Jesus himself tells us not to do this one thing. There is no higher authority for Christianity that the Son of Man who is also the Son of God.
Looking back, if GOD is really Ultimate Reality, and you're an unbeliever or especially if an ardent atheist, then you might have over and over again committed the unpardonable sin of blasphemy against the Holy Spirit, and hence they should shudder at the eternal consequences. Maybe some of those spiteful forum posts that solve nothing but blaspheme in this way, are not only pointless and fruitless, but damage you instead of others.
"30“Whoever is not with me is against me, and whoever does not gather with me scatters.31And so I tell you, every kind of sin and slander can be forgiven, but blasphemy against the Spirit will not be forgiven.32Anyone who speaks a word against the Son of Man will be forgiven, but anyone who speaks against the Holy Spirit will not be forgiven, either in this age or in the age to come. Matthew 12: 30-32
We are condemned if we say that, "That wasn't God acting [through the Holy Spirit], that was just random chance. " Or if we say, "There is no God acting as the Holy Spirit." Instead of thinking we can bargain with God, and reduce the supremacy of God into something "we control" versus being the servants of God, then we delude ourselves.
http://christiananswers.net/q-eden/unpardonablesin.html
Respected Christian theologian Dr. F.F. Bruce writes,
“…Speaking against the Son of man might be due to a failure to recognize Him for what He is. So Paul recalls how in his pre-Christian days he thought it his duty to oppose the name of Jesus of Nazareth. But if, having seen the light on the Damascus road, he had deliberately closed his eyes to it and kicked out against the goad which was directing him into the true path, that would have been the sin against the Holy Spirit.
The Holy Spirit persuades and enables men to accept Christ and enjoy the saving benefits of the gospel [John 16:8; 1 Corinthians 2:12-14; Acts 7:51], but if anyone refuses to submit to the Spirit’s gracious constraint, preferring to call good evil and evil good, how can the gospel avail for him? The deliberate refusal of the grace of God is the one sin which by its very nature is irremediable” [F.F. Bruce, Answers to Questions (Grand Rapids, Michigan: Zondervan Publishing House, 1973), pp. 46-47.].
“Anyone who rejects the Holy Spirit’s convicting influence and does not repent will not be forgiven, ‘neither in this world, neither in the world to come’ (Matthew 12:32)” [Ray Comfort, “The Unpardonable Sin,” The Evidence Bible (Gainesville, Florida: Bridge-Logo Publishers, 2001).].
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The Bible is filled with examples of people who receive forgiveness for all manner of wickedness, for ‘the Lord’s hand is not short that it cannot save’ (Isaiah 59:1). God’s boundless grace prompted Paul to exclaim, ‘When sin increased, grace abounded all the more’ (Romans 5:20). And Paul’s personal testimony showed God’s redemptive purpose and power were not limited by man’s sinfulness, thus encouraging those who feared they had sinned too grievously to be saved (1 Timothy 1:15-16).
While God’s ability to save is boundless, the Bible clearly shows that there are certain conditions under which He will not save. For instance, God will not save those who neglect or despise Christ’s sacrifice in an effort to find an alternate salvation plan.
‘For if we go on sinning willfully after receiving the knowledge of truth, there no longer remains a sacrifice for sins’ (Hebrews 10:26).
This warning pertains to those who ‘trample under foot the Son of God’ and regard His blood as unclean (Hebrews 10:29). God the Father has appointed His Son’s sacrifice as the sole way of salvation and will not grant salvation to those who seek it by any other means."
Some sins can be forgiven. Jesus says one sin cannot be forgiven. Other sins are mentioned as interfering with salvation. You are making the intellectual leap about these sins as if they will condemn someone to the Lake of Fire in the second death. Are you sure about that, or does it mean that those sins are unable to be forgiven?
We risk the second death in the Lake of Fire by every empty word, but God doesn't necessarily cause us to be cast there. Who can know? You don't take GOD on your own terms, but as a servant to a Master.