The main problem is that some people decide what's good and what's not online and paint with the broadest brush possible. Spamhaus, sadly I say, is used by a lot of providers as gospel and a lot of innocent sites are hurt.
These people have put in place a high quality method to discriminate spammers. I've been around since their beginnings, and their list has been incredibly successful (very high quality) for me, compared to njabl and other "dynamic" lists based on honeypots, or backlash entirely (say hi to spamcop).
You would also recognize that you can just as well tag the message with "likely spammminess" for use along the chain, and people would still complain that your "legitimate" message was tagged as spam by SOMEBODY, while you wouldn't complain if it was tagged as spam by a learning algorithm.
In short, people would complain anyway, except that spamhaus is doing real damage to the spammers (as in "the mail really didn't go through") and reducing their revenue, and thus forcing them to come out which such measures. Not that they will accomplish anything anyway. Spamhaus helped stop a lot of known/professional spammers, and I applaud them for that.