The fact that he asked you "I probably shouldn't right?" reveals all I need to know frankly...
I struggle with the higher power idea so had to define it my way... it's that little voice that cocks an eyebrow and say s "Dude, Really?" when I contemplate something stupid.
Sometimes a question is a statement but hell, if he asks a question it isn't meddling to say what you think.
One other thing... Are your finances comingled or seperate? You said he can't afford it and y'all are contemplating marriage, right? Has he saved for a ring and honeymoon? That was a little five figure blip on my budget last summer. If he hasn't started saving for those yet has money to go to Costa Rica for a week of male bonding then... no need to finish that thought is there?
Now if your funds are comingled then the "it isn't up to you" stuff is out the window and you have every right to say hell no unless it's from his seperate play money and he's taken care of his share of joint responsibilities.
To each his own... One of my closest friends went on his son-in-law's bachelor party and sat on the bus when the guys went into the strip club, it just doesn't fit his values. An hour or two later the groom was thrown out and had a black eye, he and his buddies were hungover and beaten up at the wedding. Charming.
...not judging, I've been to the titty bars when I was younger and have no problem with it... heck, my wife has gone to them with friends before and got all the attntion from the dancers so if I went I'd bring her - I'm not a prude.
I guess I just have an issue with the whole "I need to go nuts and get it out of my system before I get married" idea. Depends on the friends too. If you believe they are the sort who would go out to the clubs and watch boobs, drink, smoke cigars, scratch and then go home (domesticated) then it's harmless enough. If you think they are the type who would be getting hookers and losing all common sense then maybe he needs to hang around some big boy friends before he takes on marriage? LOL - So are his friends the guys in "Hall Pass" or the guys in "The Hangover"? ....in any case, make sure nobody named Alan is going.
For those who did not see the movie, listen to the words of "Alan Town" parody of Billy Joel's classic.....
The Hangover Part 2-Stu's Song (Alan town) - YouTube