Because less than infallible authority is better than no authority at all.
If one crawls, parched, through the desert, is it wise to refuse a glass of water because it smells somewhat of chlorine? If one clings precariously to a cliff, should one refuse an offered rope because it looks frayed?
Well, now you’re asking the “why” question that more properly ought to be asked of God, not of me.
You seem to approach the question from the point of view of what you want. That is, your inner monologue is telling you, “My salvation depends upon having perfect, unsoiled information regarding God’s will for me. God knows this, and wants it for me. Therefore the means through which I obtain my information regarding salvation must be infallible.”
It may be comforting to reason this way, but unfortunately you’re prescribing a modus operandi for God based on what you believe you want or need. That is, you’ve chosen a conclusion and then constructed a line of reasoning with its attendent premises and conditions in order to arrive at the desired conclusion.
I approach the problem from the basis of observation. I note that everyone seems to be fallible, including those who profess divine inspiration, be he Joseph Smith, Moses, St. Paul, or Rev. Schuler. Based on this, I simply conclude that fallibility and divine inspiration must not be mutually exclusive, else all claim to divine authority must be false. I don’t profess to know the why and wherefore. I simply observe the state of things and conclude that since this state seems to have persisted throughout Christian and Jewish history, it must be all right for it to be that way.
The dilemma is resolved by noting that even fallible people often get things right. Fallible doesn’t mean bumbling or necessarily erroneous. It means simply an absence of the assurance of correctness. Moses committed an error which offended God. He was fallible. Yet at other times he conveyed the will of God to an extent believable by Christians and Jews. God didn’t have to wave the magic wand and remove Moses’ capacity for error in order to use Moses as his agent.
I’m not especially interested in the philosophical implications of this. I don’t profess to be wise or inspired. I merely wish to see that Mormon claims are not rejected on the basis of arguments which would also dismiss mainstream beliefs.
Jab1’s argument might be expressed in the following syllogism:
People who make errors cannot be divinely inspired
Joseph Smith committed an error, therefore
Joseph Smith was not divinely inspired.
Replace “Joseph Smith” with “Moses” and you’ll see the basis of my objection. The syllogism is said to hold for Smith, but not hold for Moses. Therefore the syllogism is not valid. It is my argument that the syllogism is not valid because I observe the major premise to be untrue.