If they conducted an audit of the policy taking into account its effects on all areas of the business, they'd probably determine it was a waste of time and money, and adopt a more laissez-faire attitude as Dell, HP, and even Apple do.
It irks me when people see corporations as these cohesive entities that only ever act with deliberate intent. In reality, if you conducted a survey of Toshiba staff, I'm sure a sizeable number of them would disagree with this policy.
How else should we see it? Corporations are an abstraction layer, they're supposed to hide their inner workings and present one face to the customers. Hell, a corporation is a (legal) person. So I don't see a reason to not treat it as an whole, abstract entity - it's the corporation's job to figure out which internal part is causing them to have a bad name.
I see it as it is; a constantly morphing organism, made up of thousands of people with conflicting interests and ideas, trying but often failing to present a cohesive image of itself to the public.
We see arguments similar to yours when the subject of the Sony rootkit fiasco comes up. "It's not Sony's fault, it was just a rogue actor in a subsidiary." Um, no. The CD says "Sony" on it. That means it's Sony's fault. They spend a lot of money on branding and advertising to make sure that no one ever forgets that.
So let's not forget it.
The way I see it, companies seek to use brands to exploit irrational consumer behavior, to increase their revenue beyond the level that would prevail in the absence of brands.
Yours appears to be the equal and opposite reaction to this; attacking brands and urging boycotts so as to decrease their revenue below this ordinary level.
I am advocating the middle way. Don't pay over the odds for a brand name, but equally don't boycott products or services just because you don't like the brand.
Basically you kind of have to take both positions. Knowledge that a company is made up of bickering idiots doesn't excuse the company from acting coherently. But ignoring that fact while trying to analyze and predict a company isn't very useful either.
Those three go to a lot of effort to be consistent, and accurate before issuing public communications.
I am reasonably certain (let's say 90%) - that Toshiba put some effort into deciding that their policy, as a whole, would be to shut down third-party distribution of their service manuals. This is not the case of an overly enthusiastic legal department. This is their company policy. Suggesting otherwise is giving them credit where it is not due.