Why do I get the impression that most, if not all, opera afficionados are against singing competitions?

I am not against singing competitions. Those entering the competitions know that professional singers and opera company directors are in the audience. There is a very real chance that if a singer does not win the competition the singer will still have been heard by the opera company directors and may be able to secure a contract. Of course, a singer who wins a prestigious competition has a better chance to secure a contract at an opera company.