This is a quote from the book "On Zero Confirmation Transactions" by Chris Pacia
...e people who blocked the double spend relaying cite the above attack as a reason why no one should use zero confirmation transactions. Nevertheless, companies were able to accomplish the same th ing by just maintaining a large number of network connections, which is more of a burden on the network than double spend relaying would have been.

Now you will often hear straw man
arguments like “only the blockchain can prevent double spends, that’s why we have it”. Of course, but notice that we aren’t talking about preventing double spends, only detecting them. ...
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