Why can I only select one alignment?
Solution 1:
Yes, some classes are restricted and they are as follows:
Fighters:
- Berserker - Chaotic or Neutral
Rangers - Good
Paladins - Lawful Good
- Blackguard - Evil (fallen Paladin)
Clerics:
- Talos - Evil
- Helm - Neutral
- Lathander - Good
Druids - True Neutral
Thief - Not Lawful Good
- Shadowdance - Not Lawful
Bard - Neutral
Monk - Lawful
- Sun Soul - Lawful Good
- Dark Moon - Lawful Evil
Barbarian - Neutral
Taken from Baldurs Gate Wikia and GameFAQ