Nice coverage of C/D/E.

You said:
"I don't understand how I should realize the author refers to the
"impracticality" mentioned in the next sentence rather than to the "emotional" in the previous one."
Foul ball --- the author DOESN'T say "emotional" in the previous one. The author says that humanists are "INTERESTED in nothing more than emotion and sentiment".
I could be very interested in violent sports. That doesn't make me violent or athletic.
Many neuroscientists are undoubtedly INTERESTED in emotion as well, but they may conduct their inquiry using facts/observations/data, rather than "the vagrant fancies of an undisciplined mind".
"Vagrant fancies" and "undisciplined mind" conjures the notion of 'ambling, unfocused, distracted, unorganized' thinking. That's really not a good proxy for "emotional".
Someone wildly emotional might be VERY focused, such as an obsessed lover or an aggrieved fired employee.
Finally, you could lean towards impractical given that you get TWO reference to it ...
line 30 says that humanists serve no function for "practical" survival
and line 32 identifies the enemy of the humanist as "the pragmatist". (Pragmatism is the opposite of idealism.)
Hope this helps.