Some of those fat girls they use at the bottom of the human pyramids would make some really good linebackers and linemen in my opinion. If women are good/fat enough to play then let them play because id rather have a 390 pound larda** named Sally cover my blindside then 150 pound Nelson who belongs on the bench....
Before puberty,sure if there isn't a clear disadvantage for the girl.But after puberty there usually is a clear disadvantage favoring men.I think it really depends on the sport as well.All full contact sports seem completely out of the question, maybe except for a few positions in full contact sports like..(hockey goalie Manon rheaume) or (NFL punter or kicked)...Even in those positions though there still at risk.Another problem would be getting men to accept women as an equal and not going easy on them naturally ..Which most would probably do..Baseball and basketball on the other hand.I think if a women has the skills to compete(and not just as a political sideshow)then I'm all for it..
Speaking in opinions, I would be very uncomfortable being on a football team with a woman. It's not because I'm sexist, it's because I don't want to be rolling around with a woman, on a relationship level especially, much less trying to tackle one, which, by the way, hurts.
On another level, woman just are not as strong as men, nine times out of ten, a grown man versus a grown woman is an unfair match. Men have more physical prowess, sorry feminists;
263 kg = mens lifting record
187 kg = womans lifting record
3:32.07 = mens 1500m
3:53.96 = womans 1500m
Boys are genetically more powerful and are stronger than girls therefore it risks injuring the girls and also puts the boys in an awkward situation. They might feel uncomfortable being particularly aggressive while they are playing at the fear of harming a girl (not saying this is right but likely to occur).
Therefore girls and boys should play separate sports where it is more fair for them to perform to the best of their abilities.