I have no fantasies....only memories!
Its all up to the people in the relationship. If they are ok with it then thats fine. If one is not then they are not fine. That simple. If one person thinks is "dangerous" but is still ok with it then both should be ok with whatever happens.
I think guys have always the SEX radar on regardless of if we act on it or not. So to say "nothing is gonna happen. I know myself" is stupid because you cant see the future. you might know yourself but you dont know the other person nor know what could happen.
I am no saying is right or wrong cause I dont believe in that. All I am saying is that you must be ready to accept whatever happens.
I personally think is better to have that kind of relationship that way you dont have to worry about your significant other(s) just go with the flow. It should all be defined in a contract-like statement where all the parties express what they are ok with and with what they are not. And that contract can be redefined as the relationship and the self evolves.