[RPG] Can the Protection from Evil and Good spell be used on the caster

Pathfinder states that each spell of the Enchantment school as well as each Pattern and Phantasm spell in the Illusion school is Mind-Affecting. See Mind-Affecting^D20PFSRD definition and the Magic^D20PFSRD chapter for reference.

Mind-Affecting
Enchantment spells affect the minds of others, influencing or controlling their behavior. A mind-affecting spell works only against creatures with an Intelligence score of 1 or higher.
All enchantments, illusion (patterns), and illusion (phantasms) are mind-affecting.

So it seems more like a definition of the Enchantment school instead of the definition of the Mind-Affecting descriptor.

Protection from Evil, as you pointed out does not mention the Mind-Affecting descriptor, but states that:

[...] the subject immediately receives another saving throw (if one was allowed to begin with) against any spells or effects that possess or exercise mental control over the creature (including enchantment [charm] effects and enchantment [compulsion] effects). [...]

If we accept these two assumptions:

1. The Mind-Affecting definition does not only refers to Enchantment and Illusion spells (and the Necromancy-tied Fear seems to suggest so).
2. An effect with the Mind-Affecting descriptor is eligible to get a second saving throw under a Protection from Evil spell.

Then the answer is Yes.

Note that this answer specifically address your citation of the Fear's Mind-Affecting descriptor. One could also argue that, as long as the Protection from Evil wording is concerned, a Fear actually triggers the abjuration spell's condition outright because - in fact - it exercise influence over the target's course of action.

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.