I am sure that that in the part of the world were you live employers ask applicants. What can you bring/aport to our organization? What would their response be?
Usually something like "I'm highly qualified and can do a very good job."
In this case the requirement is that they be Catholics. Consider that part of their functions is to represent the Catholic Church that has it tenets base on the Bible and excludes homosexual as member of this institution.
Baloney. Their job is to represent the Catholic Church. That job ends at the end of the working day. Your way of thinking on this issue was generally abandoned decades ago.
Would it be right for PETA to require any employee to be a vegetarian? If photos surfaced of one of PETA's office cleaners eating a hamburger at a family barbecue, would they be justified in firing the cleaner with cause?
And here's one with a personal connection for me: my grandfather worked for the City of Toronto. During the 30s and 40s, the City had a policy that employees were prohibited from owning land outside the city limits. The justification was like what you describe for the Church: the City decided that its employees were its representatives 24 hours a day, so they should live in the municipality they served.
After WWII, the federal government gave gifts of land to veterans. My grandfather was offered a parcel of land in what is now "cottage country" north of Toronto. He had to refuse it, because taking the land would've meant losing his job.
Do you think that the City of Toronto was justified in having this policy in place?
How about the policy that many airlines had in decades past that all flight attendants had to be women, and had to be unmarried? Was this reasonable?
My aunt worked in the head office of a grocery store chain. While she was there (I believe in the 70s), two of her co-workers were fired for buying groceries from a competing chain on their lunch break. Was this reasonable?
Personally, I don't think any of these examples are reasonable. I think that the Catholic Church's stance on this issue is unreasonable on the same basis.
This is not an issue of discrimination, but a requirement of the functions that the applicant will have to succeed if hired and this would disqualify a guy person.
Gay people con not be Catholic, thus do not satisfy the criteria for a job in the Church, I suppose that Catholics are exclude from applying for a position with a gay organization.
No, they're not. "Being Catholic" is not a reasonable grounds for excluding someone from employment with a gay organization. By the same token, "being Catholic" is not a reasonable requirement for jobs with the Catholic Church.
There may be a limited number of positions within the Church where any valid applicant winds up being Catholic by default - e.g. priest: being ordained is a valid requirement for the position of priest, and it's impossible to be ordained without being Catholic.
However, this doesn't apply to other positions. Teachers, accountants, cleaners, air conditioning technicians, and lawyers (along with many other professions) can work for the Catholic Church and do just as good a job whether or not they're Catholics themselves.