Challenge 4

I think I may have already talked about this particular lesson, in this class, but I want to choose it again for this challenge; a few weeks ago I did a "Periodic Table Battleship" activity with the students, where I hid my ships on the PToE and gave them hints on how to find them.
The hints were things like, "my carrier is in period 5, isn't on a noble gas, and the heaviest element it occupies has 53 protons". If you know how to read the PToE, you know exactly where that ship is. I told them to take shots at my ships and sink them, but I would only accept an answer if they justified it by connecting their shot to one of my hints ("I think it's on hydrogen because you said it was in group 1, and hydrogen is in group 1", etc).
I found that a few students were willing to give it a shot, but less students than usual were interested. I don't know if I would have had more luck if I'd let them do it on their own, but it seemed like many shied away when I wouldn't let them just guess.
In a previous class that I observed, I saw students (highschoolers) asked to make evidential claims about a lab project, and their response was to stand there and stare at the teacher until she gave them the answer, which eventually she did. I did not see a single student in that class take the challenge.
My concern is that students may be afraid of this kind of argumentation, and I am not sure what to do about that. My fear is that this may be why so many people in society seem comfortable merely asserting their beliefs as fact and assuming that, that is good enough; maybe they don't actually understand that there is a difference and they're confused because they're being asked to do something that doesn't come naturally?
I know kids know how to use the word, "because". I wonder if it's easier to start by simply telling them to include the word, "because", in a way that makes sense before I will accept an answer... then eventually tell them why, rather than jumping straight to big words like, "evidential" or "justification".