Hi Augustus,
You paint humanists as being oversimplifiers, in general, the reverse is true.
Earlier you quoted from the humanist manifesto iii, but to be fair, that quote should have included at least the entire paragraph:
Knowledge of the world is derived by observation, experimentation, and rational analysis. Humanists find that science is the best method for determining this knowledge as well as for solving problems and developing beneficial technologies. We also recognize the value of new departures in thought, the arts, and inner experience—each subject to analysis by critical intelligence.
I never said we should 'convert' others to humanism. My suggestion has been that we should strive for universal morals, such as the UNDHR. And I've stressed that there might be many paths to implementing something like the UNDHR. For example, I see no reason why a given religion shouldn't be able to entirely embrace the UNDHR, and probably many denominations already do.
As far as meddling goes... really? Your stance is something like: "Who are we to judge that honor killings must be stopped." ?
My stance is: "Who are you to pretend you don't know better?"
BTW, in general my approach to making such changes is through peaceful, compassionate marginalization. For example, in the US, over the course of a decade or two, we shifted the public's perception of smoking from being cool, to being unhealthy and dirty. No blood was shed in the process. This type of marginalization should be applied to those who ignore basic human rights.
Of course, marginalization alone isn't sufficient, but it's a start.
As for your last question - I'd say I agree, somewhat. Again, it's an oversimplification, and it leaves out all the wonderful aspects of life that have nothing to do with science.
I suspect (I might be wrong), that your sense of humanists is that they are some sort of robot. Like Mr. Spock. Not true! In my experience humanists are often people most in tune with nature, the cosmos, art, music, community and so on.