It won't do a perfect job, and their will be false positives, but the point is, unlike with spam in email - because of their asymmetrical following model, false positives are not nearly as much of a problem. Twitter should absolutely do this.
Twitter could easily detect spammers - by their follow history, reputation score (eg a google-rank link like SVD of the follow graph), or simple ratios like follows vs followers. It will inevitably false flag some people but that's not nearly so much of a problem.
That is, they don't have to outright ban these spammers, all they have to do is block these people from search results available for #hashtags or @replies. In the case of genuine people false flagged as spammers, they can still get their message out to genuine followers. It's not too much of a loss to be banned from search results and @reply messaging until you build your karma level a bit.
You're absolutely right twitter should fix this and do it fast. It's a goddamn shame seeing a potentially very useful public resource - like adhoc organising around #hashtags - being destroyed by the actions of a few.
tl;dr Twitter can starve out the spammers just by blocking search results.
It's not an all-or-nothing thing. Excluding suspect accounts from @-replies and hashtag search results is a nice low-key way to keep the majority of conversations going. It's also subtle enough that the spammer might not realise that no one is listening.
There are services that rank twitter users based on interaction. Klout comes to mind. If 3rd party services can measure quality, surely twitter could as well. Granted, it's only one metric, but it's a good place to start.
--edited to remove quotes around the word rank. Not sure why I put them there.
Twitter could easily detect spammers - by their follow history, reputation score (eg a google-rank link like SVD of the follow graph), or simple ratios like follows vs followers. It will inevitably false flag some people but that's not nearly so much of a problem.
That is, they don't have to outright ban these spammers, all they have to do is block these people from search results available for #hashtags or @replies. In the case of genuine people false flagged as spammers, they can still get their message out to genuine followers. It's not too much of a loss to be banned from search results and @reply messaging until you build your karma level a bit.
You're absolutely right twitter should fix this and do it fast. It's a goddamn shame seeing a potentially very useful public resource - like adhoc organising around #hashtags - being destroyed by the actions of a few.
tl;dr Twitter can starve out the spammers just by blocking search results.