What is an idiom (or an adjective) to describe someone who considers and takes sides with both of two opposing sides?
I mean someone who, for example, says that both of contrasting sides in an argument could be right.
English Language & Usage Stack Exchange is a question and answer site for linguists, etymologists, and serious English language enthusiasts. It only takes a minute to sign up.Sign up to join this community
a foot in both camps TFD This idiom describes participation with both sides:
some involvement with or support for two opposing sides.
When my friends split up, I felt like I had a foot in both camps.
Though it would not be idiomatic, the opposite would be grammatical:
When my friends split up, I felt like I had a foot in neither camp
and had lost both as friends.
Perhaps the idiom you're looking for is "sitting on the fence"? it is used to describe a person's lack of decisiveness, neutrality or hesitance to choose between two sides in an argument or a competition, or inability to decide due to lack of courage.
Is that what you were looking for?