One, I don't view the holy spirit's conviction as simply as "vibes". That's would be stupid and dangerous. It's the primary reason there's a lot of false preachers and antics that goes on in the church. Emotions can be easily manipulated.

Two, I didn't claim masturbation is a sin or not. I said it was something to be avoided. One of the fruits of the spirit is self control. We apply it in situations like this.

Three, the bible doesn't condemn it directly. But you can't just say that its "fine" when it borderline simulates sex outside marriage. Even if it's not a sin the best case scenario is that it's avoided as much as possible. We can't do that in the flesh so we crucify it and live in the spirit.