All straight porn confirms is that men like watching women and men pleasing each other. They imagine themselves in that role.
Silly woman, men love the fact that woman love their dicks. It's why guys with big dick usually have a lot of confidence (swagger). Men identify with their dicks. They're the main parts that make us men, and we like being men (most of us anyway). We love the fact that you want our dicks in you. All your panting, moaning, oh fuck-ing :biggrin1: to the point of orgasm just because of the dick that's being thrusted in and out of you. Our dicks are our pleasure sticks :biggrin1:. Pleasuring you is our main goal when having sex with you but in an almost completely selfish why, for our own pleasure and the fact that if we do a good enough job you'll let us do it again and tell your friends how good you were FUCKED last night.
But in porn the main objective is the cum shot at the end. In other words, the pleasure of the man, both the guy in the porno and the one beating off to it. If you watched alot of porn you'd know that there are quite a few where pleasuring the girl isn't even an after though. It depends on the guy. If he's a real man he's trying to make her cum as many times as inhumanly possible, but if he's an asshole (like most men are) he's trying to make her "ouch". Which I'll admit, I kinda like that to. And yes I am a little ashamed of that but I'm a real man and I'll only make a woman "ouch" if that's what she likes
And as far as the whole "imagining themselves in that role", we do do that same times but more often than not we're just watching two (or more) people fuck. And they can imagine all they want, every guy on earth (best planet in the world:biggrin1

knows his dick and knows that he is watching another guys dick go in and out of a girl that he isn't fucking. He's just masturbating. I'm sure his hand has nothing on what's between your thighs no matter how good of an imagination he has.
A more appropriate way to answer the OPs question would be to ask it differently by adding some context.
Do straight guys get turned on while watching a girl suck dick?
And the answer is yes. "But I'm just imagining she sucking my dick" STFU, no you're not. You're watching her blow dude and you're thinking "damn she can suck a dick." "She looks fine as hell on her knees sucking that dick." "Damn, dude's got a nice dick, 'big as shit. Oh he's gonna fuck her good. fap fap fap fap."
No one thinks you're gay, you just like dicks. Like dude from Superbad lol. Tell yourselves whatever you need to to not
feel or be
perceived as gay but you like dick. Because that is the crux of it. Men (a generalization, I know stfu) view being gay as being less than (see fairies). And women like men (stfu) and men want women to like them enough to let them have sex with them and maybe some other things too, but mostly the sex part:biggrin1:. And men are stupid (I know because I are one:biggrin1

so their solution is to overcompensate making them immature and giving birth to homophobia.
Example:
"Bartender, give me a drink... gemme a another, gemme a anover. Hey, who wanna fight me huh? You want some a dis? No? I aint thinks. Dat's why your girl said she I fuck her better dan you cuz you gotta widdle dick, an my dick big as shit faggot lol. HEY, WHERE DA BITCHES AT I NEED SUM PUSSY AN DIS ONE AINT TRYIN TA PUT OUT LOL. WAT?, I AINT GAY YOU FAGGOT! (punch)!!!" (Sorry, I have an over active imagination)
An extreme case, I know but as a whole we are only as strong as our weakest link. And when I say homophobia I mean ANY fear (no matter how small) of being perceived as gay.
Tahoe420 writes-
"Just because I would rather see a clean, big, thick cock fucking a beautiful woman, doesn't mean that I'm getting horny BECAUSE of the cock"
The fact that you want (<--key word) to see any dick that's not yours let alone a "big, think" one is a keen indicator that you...like...dick or cock in your case.:tongue: That doesn't mean you like men nor does it mean you want to touch or suck it, I kinda do:biggrin1:
Al7inchs_n_thick86 writes-
"if I'm getting turned on watching a nice cock it's probably because I'm thinking about my own"
1.) All I see when I read this is a "straight" guy saying "nice cock"
definition
nice:
adjective
pleasing; agreeable; delightful
No, you don't like cock, you just think it's delightful

2.) There is no "probably" if you don't know why your dick gets hard I suggest find out, experiment. Go to monstercockland[dot]com and go to the solo section and watch a few of the highest rated vids with the intent to be "turned on" for the sake of getting to know
YOU
How's that for a first post, and I was just masturbating to some porn and thought I'd check LPSG and found a thread with a premise that intrigued me so much so that I stopped beating off to read most of the post and throw my two cents in:biggrin1:. I think I'll start contributing to the social aspect of LPSG instead of using it has a tool for masturbation.:tongue: I love psychology and sociology. You guys are great!