is not even their fight so it's bad turn them into allies for a roleplay perspective?

In theory, the Ranger's charm isn't a magical ability (although it's treated as such behind-the-scenes in the game), so it's more akin to you recruiting any other party member.

The point is the animal "agreed" to help you, they "accepted the risks", as they want to assist you on your quest. Plus, in theory, a Ranger's cause is one that benefits nature, so the animal has a reason to help you.

And don't talk to me about how they're not intelligent enough to agree to any of that, cause most bears in the game have 16 intelligence, for example (and in PnP Druids can actually talk to animals, so they're intelligent enough to have a conversation, as long as you speak their language).

Minsc can turn animals into allies but most of the time they die in combat

Well, if you wanna roleplay then you should try to not let them die. Just because you have allies, it doesn't mean you should send them on "suicide missions". You can try to use them more carefully.

For example: let Minsc (+other party members) aggro the enemies first and have the animals flank afterward. They shouldn't get hit much like that. "Then what's the point?" Well, bears and lions, for example, have 3 attacks per round, so they can often tear through enemies pretty quickly (even in BG2EE, but especially in BGEE), so Minsc won't be tanking for long.

Also, fun fact: the wiki has a list of animals (that also mentions the few ones that can't be charmed) and there are some pretty good ones to charm in SoD especially (eg Rhinoceros Beetles and Displacer Beasts).

Too bad all the spiders are considered monsters... (probably cause they're all massive)