I agree that it would be a useful tool if used respectfully, but with this being a public forum nobody can guarantee that. There’s thousands of members, the likelihood of this reaction being misused or misinterpreted is astronomical and will likely lead to a lot of conflicts where people feel like they’ve been disrespected. There have been many cases where I’ve disagreed with someone here, but in all cases, eloquently explaining my views, opinions, or experiences has solved the issue without much conflict or violence.
Oftentimes, if you find yourself against an unreasonable individual, it’s best to just let bygones be bygones and stop responding to them. I feel like with a disagree reaction available, that exit would likely decrease in frequency due to someone disagreeing with the post and the OP responding to the reaction.
Using words, being respectful, and staying objective have been great strategies for me in mitigating conflict here, between myself and others but also between members. I highly recommend this approach, as we are all learning new things everyday about this hobby that we love and enjoy, and opposing experiences are common due to the nature of our pastime.
TL;DR We don’t need a disagree reaction, either disagree with someone politely and respectfully or don’t respond at all