Well, it depends on what you mean. Is a priest more likely to be a child-rapist than a non-priest? That's one question. Do rapist priests offend at a higher rate than non-priest rapists? To that the answer is 'yes'.

Or to phrase it another way: priests don't make up an unusually large share of rapists, but an unusually large share of victims were raped by priests.

The main factor in this is opportunity. A paedophile working as a taxi driver, car mechanic, or housepainter will only have regular access to a small handful of children -- his children, maybe nieces/nephews, maybe the kids of his closer friends. There aren't as many opportunities for abuse (contrary to 90s stranger-danger tapes, it is relatively rare to victimise a random kid on the street). A priest has access to far more children and for a much longer period, providing far more opportunities.

Secondly, abuse of the position. The usual MO of a child rapist is to threaten or pressure the victim to make sure they're not caught -- things like "You'll make your parents hate you", "Everyone will think you're a gross slut", "You'll get me fired and I'll kill myself", etc are common. Many people who were victimised by priests speak of the priest using very effective pressure of this kind -- talk of sacrilege, angering God, hurting the church, etc. And it's not just the priests -- in Australia and Ireland, rape victims planning to testify in court have been visited by church leaders who pressured them to drop the case for the sake of God and the church, and told them that hurting the church for any reason was disgraceful. All of this stuff means that priests are significantly more likely to continue confidently offending, with their victims less likely to speak up and come forward. They can apply pressure and guilt in a way that offenders in other positions cannot.

Thirdly, protection. The big heart of the controversy is not simply that priests have offended, but that for a very very long time, the church protected them. In cases like Father O'Grady's, the church would reassign priests accused or charged with rape offenses (or who the church themselves had discovered to be offending) to different states, provinces, even countries in addition to pressuring the victims and not reporting discovered crimes to the police. This stands in a sharp contrast to other institutions, like the teachers' unions, who would immediately burn and report members discovered to be abusing students or in possession of child porn. This, too, meant that priests continued abusing for far longer periods than most other child abusers and with more confidence.

The average number of victims for an accused priest is staggeringly high compared to the number of average victims for accused non-priests, and that's where a lot of the stereotype/image comes from. Even if all professions offended at exactly equal rates, priest victims would make up a disproportionatley large number of all victims.