I remind you that "community forum" gets a lot of attention and answers from Proxmox team members. Do you want them to still have time to answer the (community) forum or do you prefer they quit proxmox and find another well paid job?
THIS!
Repository bandwidth is not free, someone needs to pay for it.
Developers are not free, someone has to pay for them.
Compiling code takes time and labor, need more money.
Responding to questions on the forums requires labor, need more money.
Setting up a test lab is not free and requires money
The source is open and free
Maintaining, patching, fixing, testing, compiling, distributing and supporting all cost real money and it needs to come from somewhere.
They are only asking that you pay for the stable
binaries.
They still provide you free support (this forum and mailing lists), free fixing, free patching, free testing, free compiling and free distributing.
That is a heck of a lot of free they provide to anyone, what is there to complain about?
People have options:
1. Subscribe, your money supports the project, without money Proxmox does not exist.
2. Use the free repo , might be less stable, your contributions on reporting bugs and community involvement is how you support Proxmox
3. Grab the source and roll your own binaries, you still have the same open source freedom you had before this change