In this forum, where people are talking about something so personal as their beliefs and values and faith, we need to be careful not to sound like we are being invalidating about something that is so close to someone's heart. So, to the person who thinks cats are the best (remember we're really talking about expressing their heartfelt spiritual beliefs), it could be hurtful to say "I dislike cats because I am allergic to them." It isn't necessary to say anything at all against cats, or to be in any way critical of a person's stated belief. In the cat example, the person originally said "I believe that cats are the best." That is a personal belief. You may not share that belief, but you being allergic to cats is not relevant to their belief that cats are the best.