DS (12) has been playing since he was 2, DD (10) took it up last year after years of trailing round, watching her brother play. Nothing but a positive experience from us. DS had a fully 50/50 mixed team before they split into single sex teams and the boys were in awe of the girls - they were superb. If anything, it's taught him that women are very much his equal. We see the same ethos in DD's current minis team.
The culture is very much one of inclusion, respect and teamwork. Regardless of ability, everyone on the squad gets to play at least half a match at fixtures, whereas in football it's not unusual for a child to sit on the benches for a full game. Backchat, to referees, coaches, or the opposition is simply not tolerated and the children will actively pull each other up about it - this trait has carried over into DS's other sports as well as his attitude to his school teachers.
At 5, I'd suggest letting him have a go. We lost numerous players once they moved from tag to contact as many stopped enjoying it and the training commitment stepped up a gear, which they couldn't, or didn't want to, commit to. You really don't need to worry about a misogynistic, drinking culture from a bunch of 5yr olds.
Injury is a bigger concern, in fact DS has just finished a 3 week 'Graduated Return to Play' programme following concussion from a head injury just before Christmas. He's an experienced player, been well trained in how to fall, but yes, injuries still happen (although far fewer aged 5). Rugby has massively stepped up when it comes to injuries, concussion in particular, and I have never seen a group of coaches, first aiders, physios and safe guarders move so fast than when DS sustained his head injury. He went straight to A&E, I had follow up calls from the team physio and his coach for the next 3 weeks and he had to attend two GP appointments before he was allowed to return to play. Rugby takes head injuries incredibly seriously and personally, watching all the procedures kick in, I found it incredibly reassuring.
As an aside, DS is a small, lean, super fast sprinter, so he plays out on the wing - I've positively encouraged this as it keeps him away from the huge front row....worth giving some thought to 