The notion that "at least they're doing something" isn't a valid justification in my mind. There are plenty of reasons to believe that this wouldn't work, and adding more garbage certainly does make matters worse (even if by a miniscule amount, relatively speaking).
As for more promising projects, we'd be better off doing research to find those projects than throwing away people's money on a pipe dream. Pretty much any project at this point would be better- engineering bacteria to eat it, Dyson funnels to very slowly separate it out, whatever. I'm not a marine or materials scientist. I'm a person with limited funds to contribute towards things, and I don't like being sold snake oil, especially when the response to criticism is "well at least they're doing something!"