In his blog, K3NG writes that he believes the use of a proprietary audio codec as part of the D-Star protocol makes it illegal under FCC rules. I am not a lawyer, and have no wish to get sucked into that particular debate. But I do feel that closed or proprietary protocols have no place in amateur radio as they impede or prevent home construction and experimentation and are contrary to the spirit of the hobby.
But to be frank, I am against developments like D-Star altogether. Such technically sophisticated systems reduce most of us true amateurs to the status of mere users, because only professionally qualified people have the necessary knowledge and skills to actually participate in their development.
Anyone who knows what a soldering iron is can put together a simple CW transceiver. With a little more skill (or with one of the many available kits) radios capable of SSB and data operation can easily be built. VHF FM transceivers aren't hard to build either, though I'm unaware of any currently available kits. But I don't see any opportunities for the ordinary ham to get involved in building D-Star gear.
You may argue that ham radio isn't just about building equipment. But the point is not that you have to build your equipment, but that you can if you want to.
I don't see what benefits developments like D-Star bring to the hobby. They just appeal to the type of people who want to make contacts without concerning themselves about how their voice gets from A to B, the kind of people who write to RadCom and QST complaining that there are too many articles that they don't understand. Citizen's Band was invented for a reason.