can anyone explain why ... Is it just some eeeeew factor, or does it go deeper than this?
It does go deeper. As a Christian I can say that there are many things which God asks which I do not understand the "why" behind - lots of illogical stuff:
like - commanding someone to get water out of a rock
why did God tell Moses to get water out of a rock? why not let him get it out of a stream? or tell him to dig a well?
why tell him to do some illogical thing?
it was a demonstration of faith/trust...
Moses did not have enough faith btw - instead of speaking to the rock, he hit it with a rod in a sarcastic gesture, which kept him from ever seeing the promised land...
(Old Testament | Numbers 20:8 - 12)
8 Take the rod, and gather thou the assembly together, thou, and Aaron thy brother, and speak ye unto the rock before their eyes; and it shall give forth his water, and thou shalt bring forth to them water out of the rock: so thou shalt give the congregation and their beasts drink.
9 And Moses took the rod from before the LORD, as he commanded him.
10 And Moses and Aaron gathered the congregation together before the rock, and he said unto them, Hear now, ye rebels; must we fetch you water out of this rock?
11 And Moses lifted up his hand, and with his rod he smote the rock twice: and the water came out abundantly, and the congregation drank, and their beasts also.
12 And the LORD spake unto Moses and Aaron, Because ye believed me not, to sanctify me in the eyes of the children of Israel, therefore ye shall not bring this congregation into the land which I have given them.
trust/faith is the foundation of intimate relationships - if you cannot trust someone, then??? Trust involves doing things which are illogical - if it is just agreeing with someone and following your own combined logic, that is not trust - and it does not solidify relationships. (do you have an intimate relationship with your physics teacher because you agree that F=ma?)
What is logical to one person might be illogical to the next, but everyone will have their "Abrahamic sacrifice" moment (you know, Abraham sacrificing Isaac) when we decide what we are willing to put on the alter - illogical as it is - it is necessary to demonstrate faith/trust and the gateway through which we enter into a relationship which has faith/trust in it.
The falling backwards and letting someone catch you type of exercise... only there is a higher risk than just falling backwards, and a stronger trust - and stronger relationship created at the outset of it.