Bad topic spam is bad, yes, but alienating potential new users might be much worse for small to medium communities.
Maybe a compromise could work, like gating newly registered users who clicked on “Log in to Create” through a page that encourages them to read the top topics and ‘hides’ a link back to where they first clicked the log in button at the bottom of the suggested topics list? If they follow through with that they might actually have a valid reason to start a new topic… 