YES
Honestly, I see no point, reason nor value in not blocking those without accounts. Pretty much, everyone else has said much of what's already on my mind regarding the issue; this will encourage (free) membership, deter annoying and sometimes even pointless edits to pages belonging to others, deter vandalism of all kinds, reduce trolling, track vandals and so on. I see more benefit than harm with this decision, though saying there's any harm at all is blowing things out of proportion to me.
Essentially, I see it this way: Being anonymous is fine and all if you just want to sit on the sidelines and watch what's going on, but it shouldn't interfere with the wiki itself, whether by accident or on purpose. Having and maintaining present accounts is obviously for those of us who want to get involved with the community and its activities, and who want to be known on this and many other wikis. The line drawn between those with and without accounts should be painfully clear to see by everyone, and I highly discourage any opportunity to blur that line for harmful, frustrating or ourtight generally negative purposes.