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you have laid on how Bitcoin is the "solution" for double-spending just because Bitcoin's whitepaper has said it so.
I quoted the white paper to highlight what Satoshi has opened his paper with: A solution to the double-spending problem. Nobody would ever bother reading his paper if he was starting by saying hey, I got an idea about how to resist against double-spending! Money, digital or conventional, is not about just resisting such a huge problem of being potentially re-producible by spending ever and ever!
One having fear/worry on something they believe in won't really go away. The presence of just a possibility of a 51% attack happening alone just put some fear in a lot of people, seeing that there is a possible flaw on how Bitcoin transactions work and how they can be erased, reversed, and be double-spended is something that can cause fear in both the consumer and the producer side of things. Not until we reach a certain level of miners really dominating the network I guess this fear from a 51% attack won't just disappear instantly.
It is not a fear of doubles-pending, take care of the terminology, the sole presence of any kind of fear about double-spending would make bitcoin void. It is just about how a short fraudulent re-org attack can disturb people and this fear has a mitigation measure: wait for more confirmations for more valuable transactions. That simple.