I'm currently a software developer who was once a computer repair tech, who also had to take day labor jobs in college, so I have (maybe) a unique perspective on this, as I have worked several sides of this question.
As day labor, I have helped set up cubicles and other furniture in an office environment, as well as moved furniture for large and small offices. All of this requires knowledge that most people don't have. I know this because I didn't know the "tricks of the trade" until I was in the trade. In my experience, not many people know how to safely move office furniture, let alone the electronic equipment.
When I was a computer tech, I was also hired to move electronic equipment between offices. While it was easy work for me, again, most people don't know the correct or safe way to move computers, laptops, copiers, networking equipment, etc. and then set it back up. Even in this role, we were only allowed to pack up the equipment into boxes and onto pallets. The actual moving between offices was still done by a licensed, professional, insured mover.
As a software developer, I would expect to not have to do heavy labor for my employer, unless it was an emergency, such as a networking rack or part of the building falling on someone. I.E.: someone is in danger and needs rescued. They pay me for my mind, not my muscles. I learned this the hard way, by volunteering as "the muscle" for things, then getting stuck being the "goto guy" for physical labor instead of mental labor. Most people think that if you can do physical stuff, you can't do mental stuff. Because this is often true, and the fact that employers will try to "save" money in any way, you can get pigeon-holed in a low paying job for not doing the high paying duties, even if your boss/manager/CEO is the one giving you the off-topic duties and preventing you from doing your real job.
That all said, asking you to volunteer for a labor intensive, dangerous job on the weekend is a recipe for disaster on many fronts. Not only can the equipment get damages, but also the employees. This is also taking pay away from people who do this for a living, or at least attempting to earn a living. As such, it's not ethical.
Also, getting a pizza lunch for doing this large amount of work is a slap in the face.
As for the coordinator of this task complaining about not enough volunteers, that verges on workplace bullying. That depends on the context and manner of the complaint. If it was an offhand comment, that could just be frustration that the task they are in charge of can't be complete. If it was belligerent and badgering, then it's something much more problematic and less than ethical. It may still not be exactly unethical, but it's also not 100% ethical.
I wouldn't volunteer for this "task" and I think I'd even talk others out of it. This is one (of many times) the "not my job" statement is a reason and not an excuse.