The most common and most likely answer to this crossword clue is the 5 letter word SIDED
I've seen this crossword clue in The Daily Telegraph
S
I
D
E
D
Buddy explains!

The straight part
We know that "aligned in debate" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case aligned in debate = sided.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SIDED mean?
SIDED verb- To ally oneself, be in an alliance, usually with "with" or rarely "in with"
- To lean on one side.
- To be or stand at the side of; to be on the side toward.
- To suit; to pair; to match.
- To work (a timber or rib) to a certain thickness by trimming the sides.
- To furnish with a siding.
- To provide with, as a side or accompaniment.
- To clear, tidy or sort.