Being honest and well-intentioned is a property of the arguments the author uses, not whether you like the conclusion.

I disagree. I think "being honest and well-intentioned" is a property of the person advancing the argument (and reducible, in principle, to brain states), not a property of the argument itself (that is to say, a particular set of propositions). People can produce deeply flawed (invalid or inductively weak) arguments while actually trying to produce the opposite (or at least, it feels like I can).

More outlandish than monkeys changing into humans?

You are right, what is or is not "outlandish" depends heavily on large amounts of assumed background information. For instance, depending on the time period, it would be extremely "outlandish" to claim that disease is caused by "invisible animals", but moderns seem to be quite comfortable with the idea.