[RPG] Does Protection from Evil protect against the Fear spell

Yes, evil creatures can cast Protection from Evil. You can cast spells with whatever alignment subtype you want, it's just that there may be consequences. Unless the caster is a member of a class whose description says explicitly they can't do that... Like the cleric for instance. Since casting an alignment typed spell directly taps into that raw goodness/evilness/etc of the universe they just plain can't do it.

The Alignment section of the PFSRD states that casting [evil] spells is the equivalent of committing minor evil acts (third sentence).

I would say that casting [good] spells, like casting [evil] spells, has the main primary effect of pissing off your deity if you're on close terms with them. So if a good divine-type is casting [evil] spells (or otherwise committing evil acts) they may get punished, same deal with an evil divine-type casting [good] spells or committing good acts. "Hey, I thought you were on board with the program, maybe some spell failure will wise you up."

But for longer term alignment change, you're right that it's not just "cast a bunch of good spells and you're good." Even though the alignments are depicted on a symmetrical axis, they aren't. Evil is a corruption of good, good is not a corruption of evil. Some people like treating them just like they're different football teams, but that's obviously not the case in the source material of real world religions this is all being drawn from.

There's a new section on Changing Alignments that is directly relevant to this interpretation. An evil creature has a specific path they would need to follow to become good and a set of penances they would perform to get there. Conversely, there's a lot of paths to becoming evil. "Enter through the narrow gate. For wide is the gate and broad is the road that leads to destruction, and many enter through it. But small is the gate and narrow the road that leads to life, and only a few find it." Or, for those fans of the second most popular holy book (TVTropes), Evil is Easy.

See Is casting the spell Blood Transcription an evil act? for related discussion.

Yes, for some types of creatures. These abilities are found on sorcerer bloodline arcana and on metamagic feats that require being 6th or 7th level to take.

Undead

The sorcerer Undead Bloodline arcana makes your spells affect formerly humanoid undead as if they were humanoids.

Corporeal undead that were once humanoids are treated as humanoids for the purposes of determining which spells affect them.

The Threnodic Spell metamagic feat makes mind-affecting spells affect any undead.

This feat only works on mind-affecting spells. A threnodic spell affects undead creatures (even mindless undead) as if they weren't immune to mind-affecting effects, but has no effect on living creatures.

Constructs

The sorcerer Impossible Bloodline arcana makes your mind-affecting enchantment (compulsion) spells affect constructs.

Constructs are susceptible to your enchantment (compulsion) spells as if they were not mind-affecting.

Constructs are treated as living creatures for the purposes of determining which spells affect them.

A similar ability is granted by the arcana of the 3rd party Constructed Bloodline.

Oozes and Vermin

The Coaxing Spell metamagic feat makes mind-affecting spells affect any ooze or vermin.

This feat only works with mind-affecting effects. A coaxing spell affects mindless oozes and vermin as if they weren't mindless, but has no effect on other creature types.

The 3rd party Vermin Bloodline's arcana makes you treat vermin as animals when casting spells.

You treat vermin as animals when targeting them with your spells. This can make vermin susceptible to mind-affecting spells, for example.

The Vermin Heart feat (available to druids) changes which spells can affect vermin, but doesn't seem to bypass the vermin's immunity to mind-affecting effects.

Plants

The Verdant Spell metamagic feat makes mind-affecting spells affect any plant.

A verdant spell affects plant creatures (even mindless plant creatures) as if they weren't immune to mind-affecting effects, but has no effect on other types of creatures. This feat works only on mind-affecting spells.