Of course they can, but the rules are not telling them to do so.
The qualitative difference between the rules for a class saying the class loses their powers if roleplayed wrong on a subjective measure (violates a code, does an evil action) and classes that have no such rules provision seems pretty clear.
If playing an AD&D or 3e paladin the class rules say for the DM to judge whether the character does any evil act. For a fighter or wizard the class rules do not say for the DM to do so.
There can be good faith differences of opinion on how a cleric or paladin should act, the DM does not have to be out to screw you over for this to be an issue.
Nonsense, it is trivially easy to avoid the problem of worrying about PC and DM differences of opinion on the proper way to play a character under the ex-cleric and ex-paladin rules in 3e, play any of the numerous 3e D&D classes without such restrictions.