You're right on that, can't argue.
Just an addition, maybe it will motivate those casual and new players to join guilds and play WoW as it was supposed to back then, before community was killed off for good by all the QoL stuff coughraidfindercouhg. So, it may as well be a good thing.
There are much more ways to communicate and find groups to do content with nowadays than there were back in 2005 (BattleNet, Discord, BarrensChat). Regarding the loot trading, I think that's why it's unnecessary to implement it in Classic. I expect there will be a lot of groups forming by people who are playing together often and I guess there will be less ninja-ing when you're actually talking via voice chat and are playing with your group on a regular basis.
So organised groups and voice chat are my arguments. Also like the point others made of how ninjas often get blacklisted, which is very impactful on non-crossrealm servers. And if you get ninja'd, remember #NoChanges is what we wanted. It's part of the bigger picture.
I strongly think that loot trading will be detrimental to the classic feeling. I am not a strict "no changes" guy, but would like the experience to be as matching to back in the day as possible. While I understand all the positive aspects to this change and think back about how frustrating it was back in the day, I really think it was part of the game. I think a loot trading is one of the changes we subconsciously knew where probably coming. In my opinion, there should be a couple of tweaks to it, i.e. only tradeable within 15 minutes; only tradeable inside dungeon. Furthermore, I think it will not really be a noteworthy thing for guilds that raid on a big scale. In five man dungeons however, I think this will have more negative impact than positive and will result in many people not going with people they don't trust.
I agree it will probably end up not being an issue for 99% of people, and likely it will only be an issue for people who run dungeons with random people. So if they were to change the implementation of loot trading at all, also unlikely for Blizzard to do that, I guess perhaps to change it to only be available in raids.