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And it's not a question of 4th degree tear vs. episiotomy. Many women who receive an episiotomy wouldn't have teared (or only would have had a minor tear) otherwise.
No, it's a question of avoiding a SECOND major tear by having an episiotomy. It sounds like you've never had a major tear so perhaps can't understand how traumatic they are. The OP was specifically asking about getting an episiotomy to avoid a second tear. I am sure the OP would prefer to avoid both tearing and episiotomy, and the advice you shared about position and water birth is helpful in that regard.
But once you have had skin, muscles and organs stitched back up, and underwent a long healing process, you aren't eager to go there again. If I had torn the same areas again, I don't think I would have healed so well.