Forbid Not

What does it mean when it says, "forbid not to speak in tongues" (1 Corinthians 14:39)? Does it mean anything? I do not think it means we should not exercise discernment. We are commanded to do that (1 Thessalonians 5:21,22; 1 John 4:1; 1 Corinthians 12:3). But it would seem to indicate that categorically forbidding everyone to speak in tongues is questionable. Now I know the standard answer is that it is speaking of real tongues, and it is then claimed that modern tongues are not real tongues because tongues have passed away. But it seems strange that Paul would unqualifiedly say not to forbid to speak in tongues if people were required to forbid it in another twenty years or so.

Further, this only works if you can clearly prove tongues have passed away, but the Scriptures used to prove it are very weak (1 Corinthians 13:8-12; 14:21,22; Hebrews 2:4). Now it is claimed there were times when no one  spoke in tongues. But if tongues are not something required of every believer or a necessary sign of spirituality, this is not a problem (1 Corinthians 12:11-30; 13:1-3; Romans 12:6-8). God gives His gifts when and to whom He wants to give them. How much of a gap there is in terms of tongues is arguable. But even if there was one, this can be attributed to the will of God, who gives gifts as He wills; however, it does not prove tongues have permanently passed away. God caused prophecy to pass away for 400 years between the Old and New Testaments, but that did not mean it had passed away permanently. And I need to ask whether I can really know that tongues should be forbidden across the board. Particularly if God commands me not to.