Earlier quoted context omitted.
$8 won’t necessarily price out spam accounts. As a counter example, on Tinder there are many fake/spam accounts with premium membership.
But with spending money, you can theoretically have more information on the buyer which you can use to help identify and fight spammers/bots & their networks. For example, you can limit one twitter account per credit card or registered user (identified via payment method). If they are found to be spammers, you just kill the account and ban the payment account(s). They can still obviously work around this, but the cos…
This move perhaps limits spam as practiced today, but the attacks that will happen once the network changes will be different in ways that are difficult to predict.