I don't think that assertion is based on any credible socialogical survey. I get the since it's just a spur of the moment knee jerk reaction that is latent with sexist undertones and grossely generalizes the other gender. I don't think I've ever met a parent (or another human being) that advocated the boycotting of such products with a military theme and nature, but then again this is based on personal experience and I live in a fairly conservative community.
I think price, distribution, lack of marketing, quality, and competition in the toy market would be more reasonable explainations for the percieved struggle and decline for the contemporary military inspired toy and would be worth doing further reaserch on. Afterall, 21st Century toys had quality control issues and appealed only to a very niche market. Unimax did manage to sell figures to youth on occasion but their figures had a tendancy to break due to their joints being too stiff out of the box, which I suspect discoured parents from buying more. Their vechilces tended to be too expensive for the average consumer, and alot of them ended up on clearance. Hasbro never had quality issues in the since of durability but they have completly failed as a company to properly market and distribute the GI Joe brand no matter how much we decide to blame the retailers. Prefered brands and fads amongst children are typically based on what is most marketable to them right now, and the military, GI Joe, type toy just isn't the fad right now.
It is apprent to me that the concept of the military is not threaten by any percieved social trends of political liberalism, as Chap Mei is able to sell military toys to parents all year round in Toys R Us retailers. To further note, Big Lots has been selling a brand of military toys every fall and winter for the past decade almost, and even now there is a brand of offical United States Marine Corps figures on the shelves of some of these retailers. These figures are succesful despite their lack of articulation and detail due to they're availbility, low price, and sturdy, durable builds, never minding the novelty of the military toy.
To blame the decline of Unimax, and adult military toy collecting as a hobby, on liberal women seems too simplistic of an argument to me.