Originally Posted by Chris is me
I think this is 100% okay if the opponents are attempting to say "no, don't give them that penalty, they didn't actually do what you said they did". The classic example is the 2013 Curie finals, when the opponents were arguing that the red card for the other alliance contacting them while climbing was incorrect as the contact did not occur. This kind of advocacy should be commended.
I think having opponents go "no, that's a silly rule, don't enforce that please" could be the slippery slope you're warning about, though.
Either case is a slippery slope. This effectively allows head refs to second-guess the information the 4 other refs have asserted is true. Sure, the information is sometimes imperfect
*. Yet the only sources of information for an individual call should be the other event officials (referees primarily, but FTA/volunteers via solicited information as well). Video replays/etc are a totally different topic from rules about safety though.
*Initially, a red card was given to 1885. It was overturned since the ref who called the foul didn't know for sure who actually caused the gear to fall. The question we asked the head ref was "Because this will impact alliance captains, please verify which human player actually caused the gear to fall". We would have lived with the result regardless of video replay results because I understood that the source of information had to be the ref who called the foul. The video replay confirms what I had hoped was true given what both pilots told me, but video isn't something that's available to a head ref.
Regardless of which way the call went, this is a great example of a referee using judgement to confirm info with proper sources and then determining the best outcome based upon the evidence she had. Within the technicalities of the rules, she very well could have let the card stand, given it to the other pilot, or given it to both teams who had pilots.