Concerning playmo-wars:
I can understand Geobra concerning WWI and WWII as those wars have a direct and rather recent link with Germany's history, it are their fathers, grandfathers and greatgreatgrandfathers that started those wars. And people in general don't like to see diroamas filled with Wehrmacht-soldiers, Waffen-SS troopers and Nazis. Hitler himself is often considered the anti-christ, and not without good reason. So, understandable Geobra doesn't want to see any of that (in public domain).
But: what about f.e. the British Zulu War, the US Civil War, the Naopleonic Wars, the Spanish Wars in Flanders and The Netherlands, .... , the crusades and the Siege of Jerusalem, the expansion-wars of the Roman Empire, and near the start of it all the butchering by Conan and other barbarians during the Stone-Age? Those battles and wars are often depicted as well with Playmobil in dioramas, and nobody gives a cry.
Of course in "ancient" times they didn't have automatic rifles or atomic bombs, horrible weapons indeed.
But, ever seen (or imagined) how a 17th-century sailor looks after he and the deck of his ship have been wrecked by scrapnel from canonfire? Or the corps of a knight, decapitated by the sword of his opponent?
To me it is quite the same, it doesn't matter in which era the conflict took place as long as one doesn't show (to a general public) the horrors of war but just depicts the playmobil soldiers and their gear.
The reason for toy manufacturers and (most) forums to avoid certain themes is merely that these in a predictable way lead to controversies (prooved in this very thread) because and/or in which feelings of a number of people (esp. target audience (forums), customers' parents (toys) and or among those who will 'see' it (public, forums and toys)) are hurt or upset. So the avoidance of e.g. modern war is rather a matter of 'politeness' or 'respect' (if not of business alone) and has less to do with history, views on history or politics, freedom of opinion or mere amount of cruelty alone. And there is always an implicit statement, too.
Depending on further circumstances there are of course also possible serious (e.g. different legal responsibilities of forum owners and manufacturers) and other reasons. Thus 20th century and later wars are on the nono list, as well as maybe urban violence, terrorism, drug enforcement, capital punishment, even religious matters ... ACW, knights and romans are not because there will hardly anybody be claiming to be really offended or hurt. But surely they would be was there a number of complaints large or loud enough.
Basically there is no need and probably not so much demand for toys with statement that are by their nature aimed at children. And this is why all (not only german) toy brands of importance (i.e. lego, among others) do not have ww2 or modern 'counter insurgency' themes and are instead developing fairly 'balanced', non violent theme worlds or if it needs to be violent without any noticeable ideological or historical reference. I guess this was more or less true already some time before and got more important during the last years due to a greater awareness of possible issues.
