I'm probably in the minority of males for thinking this but it is an opinion shaped by my own experiences. Had I been brought up elsewhere and been exposed a different women i'd naturally think differently.
I think ONS are perfectly acceptable and okay so long as both parties fully comprehend and are okay with what it means. I know so many girls who are in tears of regret the next day because they feel humiliated and ****e (which seems odd to most guys).
Alot of women, imo, are not built for it and therefore when they do engage in it, it hurts them, makes them feel used and tricked. It's not their fault and it's not the dudes fault. A guy will never explicitly say 'i want a shag, just for one nightm you'll do, come home let me cum inside you then please leave, I'll prolly not want a chat or a hug after, in fact I may just want you to leave straight after. Don't think for one second I care about your ex, or that you have a dog and like making cakes. I just want you for one night only. I wouldn't take you home to my rents and my aspirations of a girlfriend wouldn't be with someone like you.' (of course not all are like this, i'm just describing your typical one). If you can handle that sort of casuality then go for it - none of my friends could.
A lot of the time getting a woman home and then out of her clothes requires persuasion in which case (my opinion) it shouldn't have happened at all. If a girl is out for casual sex, she'll let you know and feel free to pursue it. If she is not sure then it's better to avoid than to risk bruising her confidence and ego. If you take a girl home and even moments before entering her if she says no, it's a no. I've had girls come home with me on various occasions and just chat, kiss and sleep (maybe i'm uglier in my room light but i'd like to think a women still has a choice and can come for comfort (a lot have a billion issues they need to get off their chest and what they really crave is a hug and a heart to heart with no fear of being judged, they think sleeping around will help, but it doesn't))
I'm not answering your question well. My GFs sister has just gone through a break up and going out with her is a nightmare, she attracts sleezeballs and they insists that they are good guys to her and she goes back everytime, against our say and then calls my GF the next day in tears. For some people it isn't simply a 'drunken mistake' that you get over. It chips away at her confidence and she's loosing her own self respect. She is begining to think she doesn't deserve to 'find love' like her sister and that all guys are dicks (even though she is meant to be the better looking more attractive out of the two). She even slept with a friend of mine and I wanted to punch him after seeing her state when I realised what he was doing was within his right. All of us get up to it at some point in her life. She had agreed to go hone with her, he had gotten a shag, he was happy to give her breakfast wave her goodbye and never think about it again, where as she was falling deeper and deeper into depression.
I know you will all accuse her of being dumb and weak ( I did to start) but the more I talked to my female friends the more I realised how different our genders perspective of sex and ONS were. Where we guys (in my group of friends atleast) see it as a simple score, no big a deal, some of my female friends see it very differently as though they are being objectified or conquered. One even said she'd rather sell her body for cash than engage in sex casually (honestly) because she wasn't getting anything out of it. She craves more than to be someones quick dirty ****, she'd sooner make some benefit out of it.
Sorry for the long spiel. Maybe i'm just friends with weirdos but I think ONS really need to be defined Perhaps girls need to learn to accept them/not engage in then (which in my opinion is hardly fair at all, girls cannot help that their life experiences/mentality have shaped their sexual preferences so.) But till an equillibrium is reached, guys need to keep it in their pants in reapect of protecting our female citizens sexual confidence and emotional well being. If you can handle what comes with ONS go for it. Just stay safe and don't hurt anyone.
Sorry once again for holding such an extreme and perhaps inaccurate view of the situation, but it helps me explain and inderstand the experiences I have had/seen happening to my friends.
EDIT:
Could I just add, society seems to pressure women into thinking ONS and casual sex is a norm when in a lot of the cases it's not suited to their mental and emotional well-being. Why encourage something which is so intrinsically impossible for a large section of female society?
You are essentially tricking(?) Women into living by the rules of men (=have loads of casual sex - women are biolically designed to want long term where as guys want to spread their seed about as much as possible). Women know what you want before you engage in anything. It is OKAY to have lots of casual sex and sleep with whoever you want to long as you stay safe and out of harm from them and yourself.