Probably not. By your logic, eusocial insects couldn't evolve. The
"sterile" workers would have more offspring than the queen. Yet, ants, bees, wasps and termites have entire classes of "sterile" offspring. Basically, the sterile workers in eusocial insects are like celibate priests.
Yes, there is some cheating among workers in insect communities. Workers sometimes lay eggs which are usually eaten by other workers. Among termites, a male worker gets a small chance to have sex with the queen. So workers do provide spare genes for emergencies. However, that isn't the main benefit of sterile workers. The main benefit is that they greatly increase the chances of their fertile sisters and brothers to reproduce. Without workers to help them, the fertile siblings have almost no chance of surviving. I think this is analogous to the way celibate members of society contribute to their families.
The priest or nun increases the chances of their brothers or sisters having children. Even if they don't have children themselves, they help the parents genes survive. This is why it is usually the parents that encourage one of their children to join the priesthood or nunnery. The parents recognize, deep
down, that their celibate children will favor relatives over the rest of humanity.
This is the way it usually works out. There are exceptions, but they are few. Basically, a celibate minister ends up helping relatives survive and reproduce. Historically, this even seems to apply to secular homosexuals. By
foregoing reproduction, the celibate person helps the propagation of his
relatives.
The parents are investing most of their resources into one or two children
who are expected to have large families themselves. If they spread the
moolah out, then the chances of any of their children surviving is
much smaller.
Very often, these same parents have large families. Their economic resources are spread rather thin. The priest or nun is taken care of by
their order. Therefore, it serves as a sort of excuse.
If you look into medieval history, one sees that a minister often
holds a lot of power. Families hold on to their riches and power because
they have a priest in the family. Even a poor priest in a monastery wields
some power in the local community. He organizes people, and he gets them to
do what the family wants.
In the case of the Catholic church, the priest tells everyone to stop
using birth control. Even his own family, and certainly his community.
Although he may be interfering with the interests of the individual, by
condemning birth control he is helping their genes reproduce! Families who
listen to priests are likely to be large but very poor. The priest then "helps"
them by demanding money and resources from richer families. Even if a woman and her husband don't want children, the priest ends up "making" them have a
large family. Since religion is usually passed on through families, there is a high probability that a priest ends up encouraging his own family to reproduce.
Actually, this applies to almost all religions. Judaism, too. Hey, Jews started out condemning masturbation! The result is that the ministers of most religion wind up encouraging their relatives to reproduce beyond the individuals comfort level.
The priest also provides a safety net because sometimes he does reproduce.
You pointed this out. If the family land were spread equally between children, as it used to be in Ireland, a rich family becomes a poor family in just a few
generations. Eventually, each descendent inherits just enough land to stand upright. When this happens, the descendents run a very large chance of dying.
It is better to give all the riches to the oldest male, as was done in Germany
and almost everywhere else. All the other children have to do something
dangerous to survive (emigrate, join the Army, etc.). Thus, the youngest are more likely to be killed.
A priest is a way of increasing the chances for reproduction of the
youngest child. The priest lifestyle isn't as dangerous, unless one goes into
missionary work or something. Therefore, he drop his celibacy if the family
is getting into trouble. If he goes into missionary work, then he helps the
oldest in his family by pacifying the natives. Either way, increases the chances that his genome reproduces.
The celibate priest provides a spare descendent in case of disaster.
Further, he helps his siblings survive and reproduce.
So, no. Natural selection would not eliminate genes which make the celibate life styles more popular. Evolution counts individual genes, not necessarily offspring.