A patent license is "discriminatory" if it does not include within the scope of its coverage, prohibits the exercise of, or is conditioned on the non-exercise of one or more of the rights that are specifically granted under this License. You may not convey a covered work if you are a party to an arrangement with a third party that is in the business of distributing software, under which you make payment to the third party based on the extent of your activity of conveying the work, and under which the third party grants, to any of the parties who would receive the covered work from you, a discriminatory patent license (a) in connection with copies of the covered work conveyed by you (or copies made from those copies), or (b) primarily for and in connection with specific products or compilations that contain the covered work, unless you entered into that arrangement, or that patent license was granted, prior to 28 March 2007.This date is arbitrary. It limits the effectiveness of the protection against "discriminatory" patent licenses.
This date is NOT arbitrary. It is AFTER this clause was first discussed.There are two reasons for this. Firstly, many jurisdictions implicitly or explicitly forbid retro-activeness. Without this date, there's a good chance the clause would be declared legally invalid.
It isn't meant to protect recipients. It's intended to stop distributors.This clause fails to protect recipients from patent lawsuits, whenever the related "discriminatory" patent license was granted, or the related nasty arrangement was in place, prior to 28 March 2007. In those cases, the work fails several DFSG, if the patent licensed in a "discriminatory" manner is actively enforced and infringed by the work. It's not a Freeness issue, unless and until there are actively enforced patents infringed by the work and licensed in a "discriminatory" manner prior to 28 March 2007.
If you are a party to a "discriminatory" agreement, YOU are liable to protect downstream, or YOU CAN'T DISTRIBUTE. THAT is the point of that clause - if you want to distribute, you have the responsibility to make sure downstream can distribute too. You can't negotiate protection for yourself (or your customers) and leave everybody else at risk.
Patents are a risk factor for Americans. This clause just says you have to share the risk equally, if a distributor negotiates unequal protection then it's a violation of v3.
Cheers, Wol -- Anthony W. Youngman - anthony@thewolery.demon.co.uk