The gift of tongues is clearly biblical — it appears throughout Acts and is directly addressed by Paul in 1 Corinthians 12-14. The cessationist vs. continuationist debate is a genuine intramural Christian disagreement where both positions have serious biblical support. This is a disputable matter where the Spirit is leading the church.
Tongues in Acts 2 (Pentecost) involved speaking in actual human languages that others present understood — this is not disputed. The gift Paul addresses in 1 Corinthians 12-14 appears to involve something different: utterances that require interpretation and function primarily in the context of personal prayer and corporate worship with interpretation. Paul regulates rather than prohibits tongues (1 Cor 14:39 — "do not forbid speaking in tongues") while prioritizing intelligibility in corporate worship.
Continuationist: The gifts of the Spirit, including tongues, continue throughout the church age. The cessationist argument from 1 Corinthians 13:8-12 ("when completeness comes") refers to Christ's return, not the closing of the canon. Pentecostal and charismatic Christians hold this view, representing the fastest-growing segment of global Christianity.
Cessationist: The sign gifts (tongues, prophecy, healings as described in Acts) served to authenticate the apostolic message and ceased with the apostolic age when the canon was completed. This view is held by most Reformed and many evangelical theologians including John MacArthur and the broader cessationist tradition.
Both positions are held by serious, biblically faithful Christians. This is not a salvation issue. The excesses of charismatic practice (emotionalism, false prophecy, prosperity gospel) are real concerns that are separate from the question of whether tongues as described in Scripture still occur. Christians should engage this question with humility, study the passages in 1 Corinthians 12-14 carefully, and hold their position with conviction but not divisiveness. See the overview of glossolalia.
For a thorough evangelical overview: GotQuestions on tongues.
Questions about sin fall into two categories: things explicitly called sin in Scripture, and disputable matters (Romans 14-15) where Christians with different convictions should respect each other's consciences. Even when something isn't explicitly sinful: Does this practice reflect Christ's lordship over all of life (Colossians 3:17)? Is it beneficial — not just permissible? (1 Corinthians 10:23). Score: 75/100 Spiritually Safe.
See our Is It a Sin? hub. GotQuestions and the Gospel Coalition provide thorough evangelical analysis.