I would be careful about saying stuff like "I dont understand why its a problem", because it seems judgmental and might make someone who is really concerned who feels the need to seek help feel like they cant. Everyone struggles with temptation. Though we can overcome, its not always easy.
And I also am always worried when people who say they are struggling talk about how its hard to overcome an addiction, because even though its true, I sometimes worry that people often like....fall back on that and comfort themselves in the fact that its hard, like thinking that because its hard they are okay. You should totally feel the urge to run from the temptation, making yourself feel comfortable with it is the first step to allowing it into your life. I say that from my own experience.
And about sin and which is worse, there are things in the bible that would make one concerned about certain sins over others. Gluttony is a sin, and no one should be comfortable with it, but we are warned that sexually immoral people will not be saved. I dont know of any verses that say someone who eats more than they need to will not be saved (though I do know of a verse in romans that states people who were baptized lived in revelry of food and drink, and were destroyed by an angel of God). Totally show me if you know of one that does, though. But sexual immorality is talked out against the bible often.
No sin is okay, but sexual immorality is definitely warned against often.
And overcoming temptation can be hard, I struggle with temptation everyday. For me, I dont watch porn ever, but I still struggle with the sin of masterbation. And like you, when I do it I feel unclean and dirty. I pray for mercy when I do it, and go on my way again. But the few times I do break down, it is almost always when I wake up from sleep. Not that I try to justify my struggles with this, but it most often does occur when I am in a weaker sense of consciousnesses. I often have dreams that are tempting, and when I do wake up I sometimes have the urge of the flesh pushing at me. I do not consider sex throughout my day. I do not allow myself to think about it, and when Im awake I push it out of my mind. But when Im asleep, I have no defense. I have heard this from other Christians as well. When does it happen to you? When do you find yourself most vulnerable? Take note of it, and at those times remove yourself from your computer in anyway you can, maybe even put it in a place that you cannot reach at that time, and take time to pray.
And I like your point, Blain. Though we do slip up, and the fact that we do is a sin, and a great shame before God, He is always there to help us continue with Him, as long as your heart is on overcoming through Him, and not justifying the sin. And it is entirely possible to overcome as long as you continue to endure.
Hope that helped :3