Dear Chasid - welcome to our community!
A non-religious man once told the Brisker Rav that he doesn't believe in G-d because he has many questions. The Brisker Rav told him, "you don't have questions, you have answers". So my friend, if this question you ask is really an "answer" to why you aren't working on yourself, then I don't know if I can help you. However, I believe that the fact you are asking us this question is because you genuinely want to stop these behaviors. You just feel you need to understand more how dangerous and sinful it is, so that you can convince the Yetzer Hara to leave you alone.
There's no question that any Posek you will ask will tell you that it is prohibited. I would like you to realize that your question is really the "addiction" speaking, and that this is one of the tricks of the addiction. Rabbi Twerski, founder of an Alcoholic Rehabilitation Center, compared such claims to me once on the phone, to an addict who says "I was just trying beer, I wasn't drinking whiskey"...
As far as the prohibitions are concerned, anyone who is frum and has learned any Torah, should be aware of the severity of these sins. The Torah says "Thou shall not go astray after your hearts and after your eyes which lead you astray,". This applies to any image that arouses one's sexual inclination, and erotic images of any type are definitely forbidden. The Rabbis state that anyone who purposefully arouses his sexual organ is to be banished (Niddah 13A). The Gemara there even goes as far to say "Better one's stomach should burst than he should touch the area of his bris (and possibly bring himself to an erection)". And another Gemara says "better to walk behind a lion than to walk behind a woman". And another Gemara: "whoever brings himself to an erection is destroying the world". This is not Mussar or Chassidus, this is regular Gemara. Chaza"l were fire about this! The Medrash says that anyone who is not careful with gazing at women will come to sin with them in the end.
Viewing porn is also included in the prohibition of "Lo Sikrevu Legalos Erva, Ani Hashem Elokeichem" - "Do not come
close to revealing nakedness, for I am Hashem your G-d". There is no other Mitzva in the Torah where such terminology is used. Even with idol worship, the Torah doesn't say not to come close! Only with sexual matters, the Torah exhorts us to stay far away from it. It is also interesting to note that the Torah uses the words "do not come close to reveal nakedness" and not "to sexual relations". This implies that "revealing nakedness" (i.e. even looking) is, on some level, as if one had already done the act.
This little test can be your meter - if an image triggers a sexual twitch, a stronger heartbeat, sweaty palms, or even a silent, "Wow!" then you are polluting your soul, damaging your "Da'at," the ability to know G-d, and cutting yourself off from the Divine Presence, the Shechinah. The eyes are the windows to the soul and they are the vessels to receive the light of the Shechina. One who has damaged these vessels will not be able to bask in the glory of the Shechinah in this world, nor in the next.
So with all these sources, how can a frum person even ask such a question? The answer to this is also in the Torah.
"Ki Hashochad Ya'aver ainai Chachamim... etc..." .. "For bribes make wise men blind, and twist the words of Tzadikim". The Yetzer Hara, who offers us bribes of false and fleeting pleasures, blinds us to the obvious truths and makes us think we have real "questions". But he is just disguising them as questions. Don't be fooled, and realize that these are not questions but really his "answers"! (R' Elchanan Wasserman used this very Pasuk in an essay he wrote, to explain how the multitudes of non-Jewish wise men and scientists from around the world, fail to see the obvious and glaring hand of Hashem in all of creation).
Besides all this, viewing porn turns all women into objects of lust. This is the very opposite of what relations in a Jewish marriage are meant to be. The "lust" aspect of sexual desire was created by G-d to cause a man to seek out a woman and take her for himself. Once a couple is married, the "lust" aspect of sex should be relegated to the side and should no longer be a dominant aspect of the relationship between the two. They have dedicated themselves to each other, and when they are together, they should be cultivating an emotional bond through the sharing and sensuality of intercourse. Sex is a "sacred moment" of closeness between the two of them. This is also perhaps why Chaza"l prohibited having relations by day. Firstly, because one may see something about his wife's body that may turn him off, and on the other side of the coin, by seeing his wife's body he is fueling
his lust instead of focusing on the true sacredness of the moment.
A man who insists to make "lust" the most dominant aspect of his relations, is losing out on the true connection and closeness that martial relations should cultivate, and ultimately his marriage is likely to fall apart. As his wife has children and her body changes, and/or as she gets older, he will loose interest in her and he will never be able to lead a normal marriage life. A relationship built on "lust" quickly fades away. Also, by fueling the lust through his relations and not focusing on building the emotional bond with his wife, he will continue to be pulled after the other women he sees on the street, and will transgress all the time the Issur D'eoraysah of "Lo Sachmod". Lust is truly a poison, and the nature of lust is that "the more you feed it, the more you need it". One can never get enough of lust. In the end, either we win it over or it wins us over.
Just one last thought. Even with a strong resolve, one should never trust themselves in these areas and should get a strong Internet filter for their computer to help them through moments of weakness. And never stop davening to Hashem to save you and your offspring from what is perhaps this generation's biggest test!
Please download these handbooks that will change your life!
Right click on the links below and select "Save Link/Target As" to download the handbooks to your computer. 1) The GuardYourEyes Handbook This Handbook details 18 suggested tools and techniques, in progressive order, beginning with the most basic and fundamental approaches to dealing with this addiction, and continuing down through increasingly earnest and powerful methods. For the first time, we can gauge our level of addiction and find the appropriate tools for our particular situation. And no matter what level our addiction may have advanced to, we will be able to find the right tools to break free in this handbook! 2) The GuardYourEyes Attitude The Attitude Handbook details 30 basic principles to help us maintain the proper attitude and perspective on this struggle. Here are some examples: Understanding what we are up against, what it is that Hashem wants from us, how we can use this struggle for tremendous growth, how we can deal with bad thoughts, discovering how to redirect the power of our souls, understanding that every little bit counts, learning how to bounce back up after a fall, and so on and so forth... May Hashem be with you.