The question Can we really travel through earth's core? is wildly hypothetical - basically asking how plausible "movie science" is, from a position of ignorance - but kinda fun. Right now it has seven upvotes and seven downvotes, i.e. the community seems to be split on whether it's a "useful" question. Hence, perhaps it's worth discussing here.
We should not accept those question.
One of the rules that makes so many Stack Exchange sites so successful, is that askers must ask about a problem they actually face.
There are several good reasons for that.
One is that if one person has that problem, there's a pretty good chance that many people will also have that problem, so the answer will be widely useful. That's not true of hypothetical questions.
Another is that the asker will be well-placed to add meaningful clarifications when asked. That's not true of wildly hypothetical questions.
Furthermore, wildly hypothetical questions tend to create a lot of fluff and nonsense. That sets bad precedents, and degrades the professional appearance of the site.
Personally I don't have a problem with this type of question, as an occasional thing (my view would be different if the site was being dominated by them - but it isn't). It provides a fun diversion for those who want to read and answer it, and in this case the answers give some good scientific background for readers with a very basic level of knowledge in the field.
Wishing to try a different approach...
We are at stack exchange for many positive reasons. One of which I think is exploration of ideas. Some ideas may be unpopular at first, yet prove out valid. I think this has been the case many times historically.
I also see that the voting system we have can be harsh on people. I see some value in keeping a site "clean and serious".
But I also ask you to consider the terms brainstorming, and inspiration.
Perhaps some here have felt the frustration of understanding a concept but being able to convey it properly to a given audience.
And based on what I see as positive logic, allowing multiple +pluses to define a norm for allowing continued refinement or exploration of a question makes a lot of sense. It is the "freer" "team-oriented" approach, I think. Maybe we could encourage self-censorship or refinement where questions get down-voted heavily. Prompts to consider change or removal. Positive. Opportunity.
And sure some of us may want lean and clean and organized and clutter free. But we have ability to filter and search and sort and can easily see negative votes and consider them in our interest level tolerance. Allow some group thought to roam a little freer with the "flag" or "scarlet letter" of negative votes be enough incentive.
Encourage re-statement or re-purposing, or re-evidencing a question, whatever. Believe in the good of posters to fix if they can. Delet if they can't, defend if they can.
Hope for the best.