This is the very same requirement the Church makes of heterosexuals who present themselves for admission.
It is simply an impossibility to screen all homosexuals out of the priesthood. And, in many cases, totally unnecessary.
Since scripture writes that homosexuality is an abomination to God, I'd say that it is necessary to make every effort to prevent abominations and abominable behavior and those who apologize for and enable abominations out of places that are by oath and vow meant for sanctity and holiness.
Homosexuals and homosexuality has no place in the Catholic Priesthood, nor the Christian ministry. If a person is celibate and chaste, they would not be continuing to identify with homosexuality. By the mere fact alone -- that so many continue to do so, identify as "homosexuals" despite declaring their vows to chastity -- they identify themselves as NOT chaste.
And, there is no parallel of equality between homosexuality and heterosexuality, despite what liberal opinions demand otherwise. Homosexuality is both an abomination as defined by God in scripture, AND it represents disordered thinking.