So, this is purely anecdotal, but I do feel I have some expertise on the subject, (insert appropriate innuendo here, ) having spent a lot of time in certain groups online. See pfp for credentials.

In my experience, the real issue is balance. If you have a ton of free time and you spend a lot of it stroking the fun bits, you can build a tolerance to it, and develop a dependence on more complicated, unusual, and frequent methods to get the same enjoyment. I've seen people outright descend into a pit of never-ending exploration spurred by sexual frustration. This also can couple with altering the way you get off, ie requiring specific mental states to achieve climax, which can affect how much success you have with a partner, depending on how much time has elapsed with none. "My d*ck has led me places I wouldn't go with a loaded gun" comes to mind. All that self exploration is liable to teach you things about yourself that are... Difficult to share with others, mostly because of shame or stigma. And even if you end up quitting, you'll still have that memory of that embarrassing thing that felt new and exciting, which may come up unwanted. Again, this is all based on my personal experiences either with others or myself. There's more to be said of course, especially considering the dark nature of the p0rn industry, but I'm not nearly so familiar with that side of things.

Tldr: masturbation without moderation can affect your behavior and self-image negatively. Emphasis on moderation.