Making the mistake of throwing out the baby along with the water you just bathed it in.
Discarding something of high value along with waste.
To put it into context, Woz is arguing that the URL Spider Pro should not be banned by User-agent because it can be used to build a legitimate search index that may send traffic to your site. Because the number of search engines that will list your site without a fee is diminishing, small independent search engines built using programs like URL Spider Pro may become valuable to smaller, low-budget Web sites in the future.
Listing URL Spider Pro here in this forum makes it likely that many Webmasters will ban it.
Woz is urging caution, because banning it by User-agent may be throwing away some future site traffic to avoid a few who misuse URL Spider Pro for "bad purposes" like e-mail address harvesting. Instead, Woz suggests banning the IP addresses of those who use URL Spider Pro to abuse your site.
Although my intent was to clarify the "bathwater" saying, that's how I read what Woz had to say, and I'll welcome a correction if I got it wrong!
<edit>Woz beat me to it!</edit>