Far too many Catholics allow the issue of altar servers to be discussed as if it were an issue of secular civil rights. There is no more of a right to serve at the altar than there is to become a priest (or a monk or a nun for that matter). While I don't believe it is the only cause, the practice of allowing altar girls has been shown over and over to have a negative impact on the participation of boys.
Since the participation of boys has always been known to be a factor in discerning a potential call to the priesthood, the practice of having girls serve at the altar, while not against any doctrine, is simply imprudent. Even if most of the boys who serve won't become priests, serving at the altar gives them a look at the most important aspect of priestly life - the Holy Sacrifice of the Mass, which gives those who do have a calling the important introduction to that.
Here is a great video where boys discuss what serving the altar means to them.
To return to the topic of the "right" to do something in the Church, far too many Catholics forget that even being a member is not some sort of right we can claim. This is the whole point of the RCIA program. We don't have "altar calls" where people can just claim membership by voluntarily reciting a prayer. We have specific beliefs which must be accepted. There is a point in the RCIA program where a discernment meeting is held. At this meeting, it is not only the candidate who discerns if he wants to become a Catholic, the priest and sponsors are also supposed to discern if the candidate is truly ready - and say no if he is not.