Karma's really a proxy for community participation, albeit kind of one-sided since you don't get increased karma for up-voting someone else (and rightfully so). I don't think it would be unreasonable to say that if you don't participate, then you don't get to solicit the help of others.
But the bar is much lower than that. For the purpose of just keeping spam accounts out, I think the combination of a karma threshold with average non-karma accruing activity over time (such as upvoting others, clicking through on articles, etc) could be an effective filter.
But the bar is much lower than that. For the purpose of just keeping spam accounts out, I think the combination of a karma threshold with average non-karma accruing activity over time (such as upvoting others, clicking through on articles, etc) could be an effective filter.