Yes, but only once there is a Community ID (at least two IDs). Look for the Community ID box to the right on the observation page, and click on “Reject”
I support the original request, and it might help to deal with the problem that this option exists:
Observers opting out by default can be a very destructive option, especially if they have thousands of observations only identified to higher levels, and don’t come back to update IDs. That plant will be forever stuck at family or genus or whatever.
Another option would be to have the default opt-out apply only to taxonomic levels of genus or below. It’s hard to see a use-case for wanting to opt-out when your ID is “dicots”.