Neutral:
* Principled: This term implies strong adherence to moral principles, but doesn't necessarily imply rigidity.
* Strict: A straightforward term, but can be seen as slightly negative.
* Unyielding: This term emphasizes the person's unwillingness to compromise on their morals.
* Uncompromising: Similar to unyielding, but with an emphasis on the lack of flexibility.
Slightly Negative:
* Dogmatic: Implies a rigid adherence to specific beliefs, often without considering alternative perspectives.
* Fanatical: Suggests an extreme, almost obsessive adherence to a belief system.
* Puritanical: Implies a strict and often overly moralistic approach to life, often based on religious beliefs.
Strongly Negative:
* Bigoted: This term implies a rigid, often intolerant adherence to narrow views, particularly about a particular group of people.
* Intransigent: This term emphasizes the person's unwillingness to change their mind, even in the face of evidence or reason.
* Zealot: Similar to fanatical, but with an even stronger implication of extremism and potentially dangerous behavior.
The best term to use depends on the specific context and the nuance you want to convey. For example, "principled" might be appropriate for someone who is simply firm in their convictions, while "dogmatic" would be a more appropriate term for someone who is unwilling to consider alternative perspectives.