This is certainly the experience of the more stable provinces in central Afghanistan, where leaders talk about the need to set off bombs to receive the assistance given to their wealthier but more dangerous neighbors.
In a post titled, The “Safe Haven” Myth, Professor of International Relastions at Harvard Stephen M. Walt suggests that a re-established Taliban government is now less likely to want to offer Al Qaeda a safe haven. It would be like painting a huge target on them. He also points out that 9/11 was not planned in Afghanistan so much as in Hamburg, Germany. So maybe preventing bases in Afghanistan is not quite so important. (An answer to this opinion is available here.)
Greg Mills, a former adviser to NATO’s Afghanistan mission, while not opposing a continued involvement is very skeptical as to how the current mission is being conducted. In particular, he thinks the mission is unclear. About the safe haven danger, he writes:
If the West’s aim is to prevent the Taliban from taking power again in Afghanistan, then that might be achievable by its current actions. If, however, the aim is to prevent Al Qaeda terrorist acts in the West, then Afghanistan is probably the wrong target for three reasons: (1) Most of the terrorists in that region are “brewed” in Pakistan, (2) acts against the Taliban may incite further Muslim violence against the West, and (3) the greatest terrorist threat to most Western nations is from domestic cells.
On the left, Robert Greenwald has a documentary out Rethink Afghanistan that argues against the continuing U.S. policy in Afghanistan.