I'm sure you'll find lots of stuff to work with, but here's my little quip for your list.
The biggest (untold) problem with algae is the massive amounts of fertilizer you need. Sure you can make hundreds of tonnes of biomass on a single acre, but what comes out must go in so that means hundreds of tonnes of "algae feed" to dump into the system.
Normally not a problem except for the fact that we're having problems with fertilizer prices and supply now. Add a couple of acres of Algae farms and your depriving untold amounts of crop farms of fertilizer.
Add to that Nat gas depletion (as a source of nitrogen based fertilizer), and you have a recipe for death by bio-fuels starvation.
Anyways, have fun trolling, but don't expect any lights to come on anytime soon. As any argument you come up with can be quickly defeated by new found supplies of Unatanium
$this->bbcode_second_pass_quote('', 'a')s John suggested (feed in agri-waste), or something we haven't even thought of yet.