The fact that transaction cost money is a defense mechanism in itself. If you spam-attack Bitcoin, you just funnel money to miners, make mining more profitable, enticing more hashrate, strengthening the network.
I know you are right. It's just a pain for users in the short term, and frustrating when you see things clogging the transfer of real value.
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So you agree it can be an attack, an attack that makes Bitcoin unusable for the small user for as long as these guys can sustain the spam. This hurts Bitcoin's adoption as money.
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