I see your point, but it seems like what you want is a label "Optionally respects your freedom" or "Contains free software".But the label is "Respects your freedom" not "100% Free". To me that says "Includes a vegan option" rather than "100% vegan".The kind of freedom Grench is talking about, is the freedom to chain yourself. Sure, that is a nice freedom - it's always nice to keep your options open. The FSF or the RYF certification does not take away that freedom - just like buying a package of "100% Vegan" tofu doesn't mean that you cannot buy a steak too. It's perfectly fine to buy a piece of hardware that "Respects Your Freedom", and then install a bunch of proprietary software on it, if that's what you want to do.
But what the FSF does not allow you say, is that proprietary software "Respects Your Freedom" (or that the steak is "100% Vegan"). I think that makes sense.
If I were a vegan, I wouldn't think it were very useful to have a label "includes vegan ingredients". I would want a guarantee that all the ingredients are vegan, not just some of them.
Consider a clothes label "child labor free", and suppose you can buy an ensemble consisting of pants, a suit, and a hat. The pants and the suit were produced without child labor, but the hat was made by some 8 year old kid in some sweat shop. Would you give the label to that ensemble, saying "well, if you don't like child labor, just throw away the hat, it's an optional accessory anyway"? Would you interpret the label as "includes a child labor free dress style option"? I wouldn't.