I gave you Scripture. Paul said that tongues was a sign for unbelievers. Not believers, but unbelievers. Speaking of tongues he said, "it is written". If you go back to the place where "it is written" in Isaiah, you'll find that the unbelievers were the Jewish leadership.
1 In the law it is written, With men of other tongues and other lips will I speak unto this people; and yet for all that will they not hear me, saith the Lord.
22 Wherefore tongues are for a sign, not to them that believe, but to them that believe not: but prophesying serveth not for them that believe not, but for them which believe. (1 Cor. 14:21-22 KJV)
It was a sign to the leadership of Israel.
11 For with stammering lips and another tongue will he speak to this people.
12 To whom he said, This is the rest wherewith ye may cause the weary to rest; and this is the refreshing: yet they would not hear.
13 But the word of the LORD was unto them precept upon precept, precept upon precept; line upon line, line upon line; here a little, and there a little; that they might go, and fall backward, and be broken, and snared, and taken.
14 Wherefore hear the word of the LORD, ye scornful men, that rule this people which is in Jerusalem. (Isa. 28:11-14 KJV)
It was a sign for a specific purpose. We can't just pull a sentence from Scripture and impose our beliefs on it. Context is important. It's also the enemy of quite a few modern doctrines.