I'm not a huge fan of mandated updates, and this will probably bite Microsoft in the behind if any of those updates make noticeable changes to the end user, but it is probably for the best over all.
The typical argument that I hear is that updates break things. This is undoubtedly true, but how often does it actually happen (proportionally speaking)? If it doesn't happen very often, then the benefits carried by security updates will outweigh the inconvenience.
Some people will claim that they like reviewing updates or backing out of updates that cause problems. For the Slashdot crowd, this is probably true. For the average user though, I have to question the validity of that argument. Now I will take a quick glance at the updates performed on my Linux installation. On Windows, I gave up. Microsoft makes it incredibly inconvenient to do this, since most updates require clicking through to a KB article for anything beyond a generic description (and by generic, I mean that it doesn't even tell you what part of the system is being updated). Couple that with the large number of updates, and it is rarely even worth while to conduct a cursory review. And that is from the perspective of a technically oriented user. Similarly for backing out of updates: how many users even have the ability to isolate an update as the cause of a problem? Even for technical users, it is usually just correlating an update with the onset of a problem with no technical reason to back that hypothesis.
Ideally, Microsoft would say security updates are mandatory and anything else (including bug fixes) are optional. Realistically, I don't think Microsoft's going to do that. They have too much riding upon appearing progressive, which is hard to do when users consistently refuse to update their products. Forced updates may be a nasty way to change that perception, and has a good chance of backfiring, but to them it is probably better than the status quo.