Doctrinal errors and impenitence
If Baptists can go to heaven without repenting of Baptist beliefs that are sinful, why can't someone who commits murder or homosexual sins and doesn't repent and say they still are believers also go to heaven?
What you want to do is differentiate between saving faith that is weak, and impenitence. Impenitence over sin bars people from the kingdom of God (1 Corinthians 6:9-10).
Certainly, rejection of any part of God’s word is serious (Deuteronomy 4:2; 12:32; Revelation 22:18-19) and potentially faith destroying. Lutheran dogmaticians have acknowledged the possibility of a “happy inconsistency” when there might be saving faith in a person’s heart along with doctrinal error because of ignorance or weakness of faith, but we cannot identify this with accuracy, so we leave it in God’s hands.
Your question underscores the importance of regarding all of Scripture as truth (John 17:17) and living life in accordance with God’s will (2 Corinthians 5:15).