The author of the new digital mode software became upset with several bloggers and forum posters and decided to prohibit them from using his software and any future software projects or modes created by him. He created the software, he owns the copyright, so he do with it nearly whatever he wants. Since his software is not open source, the author can add whatever code he desires into the product, without third party scrutiny. He could easily put functionality into the software that makes it become inoperable if the callsign of a prohibited user is entered into the configuration. The software could allow a prohibited callsign in the configuration and allow QSOs to be established, however the software on the other end of the QSO could recognize the prohibited callsign and automatically terminate a QSO, thus cutting off the prohibited user from the rest of the amateur radio community and embarrassing him on the air in the process. Outside of enabling vendettas against certain radio amateurs, the software could be enhanced with more features in the future (better performance, higher speed, etc.) and such features would be given only to users who pay for a premium edition of the software.
Obviously the examples above are purely fictitious and as far as I know haven't been done, but they're certainly within the realm of possibilities. With commonly available software libraries and cheap software development tools, most anyone can create a new digital mode today and as we've seen it doesn't take much for a new digital mode to "go viral" like a popular YouTube video.
I'm not an open source fanatic, but we're setting ourselves up for some bad scenarios if we continue to adopt closed source software and proprietary algorithm modes. Will ARRL or some organization take a stand against this? Or are we going to continue to drink the Kool Aid just because it tastes sweet?