I think the main argument for celibacy is that an unmarried man can devote all his time to caring for parishioners,.
I've heard that, but I think the actual argument is slightly different. It's not just his time caring for parishoners. It's his whole focus and thought being directed toward God and/or the Church, without distraction. A married man will put his family first. The Church wants him to put the Chuch first. (Oh...uhhh....I mean God first, and the Church second. Yeah, that's it.)
For example, if a new priest is needed for a parish in Poughkepsie (sp?), right now a bishop can call up a priest in Schenectady and tell him to move. OK, boss. No problem. Suppose, though, that were a married man he was talking to. All of a sudden his wife would be up in arms that the kids would have to be pulled out of school and she wasn't going to move and you tell that bishop that you aren't moving.
Not to mention just the fact that priests are expected to spend large amounts of time doing nothing but prayer and meditation. Do you think a guy with two children under 6 is going to spend four hours a day chanting rosaries?
Of course, the problem with this total devotion system is that it's totally abnormal and unnatural. Normal people want to have sex partners, mates, and some sort of family life, usually including children. By insisting on clerical celibacy, the Church is creating a bizarre situation where only people who are a little bit off ever join in this system. Then, they tell them that any outlet for sexual urges is sinful, which adds even more anxiety to their situation.
I think more and more people are starting to understand just how bad the whole system is. Also, the most common aspect of sexuality that people had to hide from in days past is homosexuality. It has been understood for a while that a large percentage of priests are gay, although church leaders don't like to talk about it. As it becomes more acceptable to be gay, fewer people are finding the need to hide from their sexuality and seek refuge in the priesthood or a convent, and it's getting harder to fill the ranks of priests, and there just aren't nearly as many nuns as there used to be.
Of course, pedophilia is still unacceptable, so guess who joins the priesthood?
Then, people expect clergy to help with problems in family life, and more and more people are realizing that some guy who voluntarily gave up family life might have a hard time offering sound advice. (Aside: Bill Maher once said, "What's up with 'Queer Eye for the Straight Guy.' If I wanted a gay guy in queeny clothes telling me how to live my life, I could just go to Mass.) This makes parishoners less likely to support the structure of the Church, because they see less value in it.
For all these reasons, I think priestly celibacy's days are numbered. Of course, these things take time. The Roman Catholic Church has been around for 2000 years, plus or minus a century or two in the organizational phase. It might take another century or so to make a change so big.