Originally Posted by Zorg
You assume that is a bad thing. That's the thing about aliens - their worldviews are, well, alien to us.
And the teachings of the Imperium are to know your duty and to follow and obey, not to aspire (source: various inc. numerous Thoughts For the Day). Many canon sources have people wanting to join the guard to leave their homeworld as they will have opportunities on new worlds that they won't on their old ones.
Firstly; Depending on what you take to be the case on the Tau, it may be a world-view alien to them, too. YMMV of course, depending on what sources and inferances you consider canon at any given point in time.
Secondly, yeah, the doctrine advises against aspirational, break the mold thinking to some degree, but you also give an achievable example of something that can
be aspired to. Dislike your boring old planet? Aspire to join the guard/a rogue trader/etc to get away from it.