The phrase "knocking props out" typically refers to the act of dismantling or discrediting someone's argument or position. Antonyms for this phrase would include "supporting," "upholding," "reinforcing," and "validating." Instead of attacking someone's argument, these antonyms suggest providing evidence and reasons to defend or justify it. Other antonyms might include "agreeing with," "endorsing," or "approving of," which indicate a willingness to accept and support someone else's position without necessarily needing to argue against other perspectives. In various situations, different antonyms may be more appropriate or effective for conveying support or agreement rather than opposition or conflict.