I can get back to you with scientific evidence in 2 months, going to be doing a psychological study of online pornography addiction.
But this question is not only a moral question, so don't be discouraged if people think you are "over-righteous" in being careful. Porn consumption in excess, like everything else, can affect your physiology, brain plasticity (neurons and neurotransmitter), behaviors, cognition (cognitive biases in attention, working memory, decision-making), and emotion regulation.
Moreover, porn is an activity about aesthetics and values. You are constantly adjusting and adapting to societal standards of beauty and sex acts. For instance, if there is a bias in the mainstream porn industry favoring, oh I don't know, white-middle class-jock-looking guys doing doggie style, then you are more likely to internalize that as archetype of beauty and normal, and eventually it becomes high on the list of what you value in interpersonal interaction.
I.e., your attraction and affiliation in real life may be swayed by the type of porn you consume, but you don't have total control over the porn you view no matter what you think (unless you are the one making the porn), that means your values/aesthetics/behavior/emotion/cognition is to some degree at the mercy of someone else. But this is true of anything, schooling, TV/movies, music, etc. Just that porn taps into something more salient and private about your quality of life and definition as a person.