And what do people have with all that Open and Closed Source Stuff? Seriously, as if anyone would decide to "just" modify MFFS Code to fix a Bug (unless its a Team Member ofcourse). It doesnt make any sense to rage about closing Source, when almost nobody uses the open Source at all.
Product labeling. Basically, "He who controls the code is he who controls the digital product." For Open Source, it's a product controlled by all the consumers (in this case, the Minecraft community). For Closed Source, it's a product controlled by a single person or group enitiy in which to manage a product.
Since Cal created a Closed Source product from an Open Source work, people became displeased with his actions. It was an act in which people perceived Thunderdark was taken advantage of, as he could not maintain his version, and someone created a version that they could maintain, but licence much differently. It's also a prime example of the vulnerability of Open Source in general, and why business tend to not use it.
Personally, I'm just glad to see ThunderDark promoting this version of his mod, as these authors wish to keep this 'label' of MFFS within the context of IC2. And those block textures do look pretty fancy, lol...