Could you elaborate on when you mean by “controversy” there? Maybe I’m missing something but I don’t see anything controversial in the mailing list you linked to. Except some guy wants more things to be open source than they are.
The RISC V is an open, free to use, specification for a processor instruction set architecture. One can build processors in ASICs or FPGA or whatever that comply to that ISA specification and use them however one likes without any cost, licence, royalty, patent, worries or any strings attached.
RISC V does not imply anything about the openness of the processor design that you or anyone else comes up with. There are RISC V implementations that are open sourced, there are RISC V implementations that are closed.
As far as I understand the SiFive devices are implementations of the Open Source RISC V design they use. But they may contain other closed IP blocks within the SoCs. Please correct me if I am wrong.
One can liken this to the situation with C/C++ compilers. The C/++ language is an internationally standardized and open specification. There are open source implementations of C/C++ compilers, like GCC and Clang/LLVM. But there are also closed source C/C++ compilers.
Or we can liken it to the Linux kernel. Linux is an Open Source OS kernel but most of the world is using it with some closed source drivers and often firmwares for various devices. From WiFi adapters to graphics cards.
Where is the controversy in all of this? Seems clear enough.
Certainly we all want more things Open Sourced. Ultimately everything. That may not actually be totally possible at this time.