But science isn't about words like "exist", "true", or "false". Science is about words like "Frozen water is less dense than liquid water".

Only because the force of the word "exists" is implicit in the indicative mood of the word "is".

Come on people. Argument by analogy doesn't prove anything even when the analogies are valid! Stop it.

But they can help explain what people mean, and they can show argument prove too much.

• The flowchart in the original post has many endpoints about what morality might mean.

I could draw an equally complicate flow chart about what "truth" and "exists"/"is" might mean.

• There seems to be no universal consensus on what specific actions are moral and which ones are not.

The amount of consensus is roughly the same as the amount of consensus there was before the development of science about which statements are true and which aren't.

• People have strong opinions about morality despite the fact that statements about morality are not subject to empirical validation.

People had strong opinions about truth before the concept of empirical validation was developed.