It's not the default. The default is blank. It just so happens to be the first item in the list though.
Then change it to Spammer. The bots will grab it and we'll know. A human won't and he'll be safe.
I think that most accounts are in stealth mode for a couple of months before posting, right??? Not really sure, it's not something we have the ability to track.
Another question, then:
What benefits do stealth (non-contributing) members have that non-members don't have? Is there a reason to sign up if one isn't going to post? From the member's and community standpoint, not the business standpoint.