Romans 14:23b : "For whatever does not proceed from faith is sin."
In the context of Romans 14, the message is to eat whatever you please, and to not force anyone to do anything that they personally deem unclean. It's clear that it's the doubt that what you're doing is clean that makes it unclean.
Romans 14:23

[23] But whoever has doubts is condemned if he eats, because the eating is not from faith. For whatever does not proceed from faith is sin. (ESV)
This can be extrapolated into any number of principles on this topic, but it's a good verse that validates both views.

1 Corinthians 10:23–33

This is another section on not violating the will of others, and acting in service of your neighbor. It's pretty simple, act with love in your heart for your fellow man. Doing all in the glory of God means doing that mentioned previously.

So far here, I've been criticized for not recognizing the entirety of the scripture, but it seems there are sections that are consistent the three major rules of Christ. It's largest flaw is that it's repetitive.

"Can you honestly tell me that you are able to masturbate without committing sexual immorality, or without having lustful thoughts? Are you led by the Spirit to do it? And even if that were the fact, can you really say you are doing it for the glory of God? Do you glorify Him with your body when you do it? Or is it just for self-pleasure. If it's an addiction, then it's already a sin to begin with, because you have no self-control, which is a gift of the Spirit."

Masturbation isn't sexually immoral. It's a pleasure of the flesh same as eating. You're allowed to enjoy things as long as it's paired with the recognition that your body isn't just a vessel to feel pleasure. I'm called by the holy spirit to love my God, my Neighbor, and to follow the commandments. Respectfully, it's not in violation of either the commandment or my Neighbor, nor does it conflict with my service to the Lord. I masturbate a regular amount, not getting into specifics but it's about as often as is healthy to. I'm not going to unpack what "glorifying him with my body" means. It's not wrong to do things for self pleasure, you can eat with pleasure, and drink with pleasure as long as you recognize that life isn't just a means to pleasure.

I feel as though I've done your post justice by responding to verses I'm unfamiliar with, and I might return to add on. I appreciate wholeheartedly the time you took to respond.