The people voting that there must be assets on both sides of the trade have clearly never played in a salary cap or contract league. Sometimes getting nothing is the best asset you can ask for.
I've been in a league like this you speak of and one where it was changed to not be legal. The way I think of it is if you can't dump players in trades, you have to find someone to take on your garbage-in exchange they want something. Result was 5-6 player trades rather than 2 but people still certainly made it work. It sure did seem a hindrance for like a week or so and was whined about, but ....never underestimate an FFers ability to make a trade. They'll work with whatever the rules are.
I think that's what the aforementioned NBA trade was too- in exchange for taking on my garbage you get...
As far as the thread, if the rules don't say, then it is legal. Put it through and then vote (or whatever the process) on a future rule change to close that loophole.
I remember a league where you had a set number of trades/waivers you could make (commish was whiny lazy as wife was preggo and...idk just came about amongst friends) Anyhow sometime late in the season, there was a five six team trade. Soandso goes to team one who send this guy to team two, who sends....according to the rules it counted as one move.
FF folks will find every loophole to make their team better. As long as it's not mean spirited, ya gotta put it through and even then....