But if some implementation of SC (I do not think SC as idea) become scam or there is a bug then bitcoins may be lost.
Bitcoin may take a knock if 10% of the coins go missing. But that would actually simply increase the value of everyone else's holdings.
Yes, I agree. There is no need/reason to HOLD bitcoins in sidechains if you do not use advantages of SC.
SideChain always use/observe original blockchain b/c mainchain gives it value. SC must preserve value of original mainchain b/c mainchain keeps that value.