DCA-
The reason that girls are allowed to play varsity boys soccer is Title IX. One of the provisions of Title IX (otherwise known as gender equity), is that institutions receiving federal money must provide the same opportunity for girls as boys. That is not the exact language, but it's close.

That means that if a girl wants to play soccer and the school does not offer a girls soccer program, then the school LEGALLY HAS to allow her the chance to play on the boys team. If they deny the girl a chance to play, then the girl has a legal ground to sue the school for gender discrimination and the school would be in danger of losing $$.

While there is talk of reforming Title IX (something I think needs to be done), as of now that is the law. Try not to take the foul personally. I'm sure that every time you tackle a girl you do not get called for a foul, and I'm sure every team you play does not have girls on it. While I understand it's frustrating (a couple of teams we played when I was with Riverside had girls on them), try to understand that you will probably win that game 6 or 7 to 0 or 1 and you might get called for a foul or two against a girl that game and in the grand scheme of your team's season, it's not that big of a deal.

While I do think Title IX needs to be revised and rewritten, I do think that girls should be allowed to play on boys varsity teams when they attend a school that does not offer varsity girls soccer.