Someone who joined your community six months ago and hasn’t made a single post shouldn’t be afforded the same status in your community as a member who joined last week but has made a real contribution.
Mark new members as ‘provisional’ – they don’t get certain perks until they have proved themselves as an asset to the community. Prevent them from having access to certain sections of your community until they have contributed in some way. Consider deactivating accounts that appear to be dormant (before you do that though, warn members before you hit the off-switch. Make one last attempt to convince them to join in. Link to irresistible content. Tell them what’s in it for them).
Just don’t give them the same status as members who are helping to make your community a success.
For more, see ‘Not all community members are created equal‘.