Disclaimer: What I'm about to talk about is based purely on anecdotal evidence and personal experience. I'm not trying to state anything as fact, this is solely my opinion.

Stereotypical Sexual Attraction.
As a straight man, I admit that sometimes I get aroused by men in porn. However, it's just the erect penis that turns me on. So when I see a man in porn, I think of this guy with no real personality, a generic body, a bland face, and a big erect cock. For me, at least, the guy has to be a sex object.
However, when I'm aroused by a girl, I have to think of her as a person. For instance, you know how a group of guys will be walking down the street and they see a girl from behind, then all of them say, "check out that fine ass!". I honestly can't do this. I absolutely have to see the girl's face first. If she looks like a sweet, pretty girl then I think "Wow she's really cute. And her ass isn't too bad either." But if her face is ugly or if she looks like a stuck up bitch then I dismiss her completely, no matter how nice her body is.
Why am I able to objectify men sexually but not women? Because when I think of a woman sexually, I have to think of her as a potential girlfriend. I have to at the very least think "she'd be a cool chick to hang out with". Even if her personality and sense of humor don't exactly match mine. There has to be some form of human connection there besides visual attraction. While yes, there have been a couple of times I've had sex with a chick based purely on her looks, I don't enjoy it that much and feel awful about it afterwards.

The thing is I'm pretty sure I'm not alone here. Out of the six close male friends I have, only one of them really loves going to strip clubs and sleeping around. Yeah, we all enjoy strip clubs for the social gathering, the drinking, and the goofing around. But is staring at naked chicks for hours "fun"? And yeah we've all had one night stands, but most of us are looking for something more to a relationship rather than a living, breathing "fuck toy".
Sexual Objectification in Porn
In almost all mainstream porn (and a lot of amateur porn) everything is fake. The actors look sub-human. The sex scenes are over the top. The outfits, settings, and situations are ridiculous. Why? The viewer needs to simply think of the men/women as sex objects.
It's because of this that I can almost never watch guy/girl sex scenes. If they show the girl as a sex object then I get put off. If they show the man as a real person then I get uncomfortable. So now, the only way I can enjoy men in porn is if it's gay porn and it's "just fucking". I need to think of both the guys as sex objects. And when I see women in porn, they need to be in realistic lesbian sex scenes (a comfortable setting, natural looking girls, intimacy, no ridiculous toys, believable orgasms, etc.).
Coming to terms with Sexuality
I know a lot of guys (especially young men) are going to come in here and say "dude, you're gay". And trust me, it doesn't bother me. I was in your shoes at one point. I remember about 15 years ago when I first started puberty and I thought completely different than I do now. I was raised in a very backwards, rightwing christian family. "God hates fags" was our family motto. Back then if you had told me that I have to have sex with a man or get a bullet in the head, I would have told you to pull the trigger.
It is widely accepted today that there is no such thing as 100% straight or 100% gay. There are tons of people out there that are willing to have sex with either gender. However, it is very uncommon to prefer both equally as life partners. There are very few "true" bisexuals. For instance, many young college girls "experiment" with other girls, yet almost none of them would ever want to get married to one.
Hell, even the comedian Ron White, a spokes person for the most homophobic society in the world, admitted this. He said that every person is a little bit gay. Why do straight men prefer seeing erect cocks over flaccid ones? Because there is at least some sexual attraction there.
Moving beyond Gender Stereotypes
A huge problem today is that men are still being raised to be proud of our gender stereotypes. Stuff like "On average, men think about sex every 7 seconds" which is horse shit. Or "Men are more likely to cheat because it's in our DNA, we're programmed to spread our seed as much as possible". Isn't it possible that men have evolved to a point where we can make decisions that go against our primitive urges? Is it hard to understand that men cheat for the same reason women cheat, because they're horrible people?
Believe it or not, not every straight man is capable of objectifying women. Would you love the idea of being able to switch off your wife/girlfriend and store her in your closet, and whenever you're horny you can dust her off and fuck her? Is that something men really want? Yeah I know there are some people who would answer "yes" but I consider that sociopathic behavior, which has nothing to do with gender. Not all men think this way, so why the hell is ALL porn made for this type of person?
To porn producers out there: Just because misogynists like Howard Stern and Adam Corolla are the most vocal, doesn't mean they speak for every man. Stop buying into all the bullshit male gender stereotypes. Not all men think alike! We're not some goddamn hive mind. We're not all one dimensional, walking clichés. So stop treating us like we are!!!!!