I am pretty sure that bitmain can clearly foreseen the profitability of the each algo before one or two month
even they can calculate it.
Unit pricing policy , proves it ,
For this reason they knew that customers would be losing money while buying D3s
I believe they should not let the profit fall below $ 400-500$
daily 6$ will destroy most of loyal customers with bitmain's competitors together
Bitmain is a very important company for miners community
I would expected them to follow more ethical and sensitive policy.
Anybody can calculate it, you just need to make some assumptions about future network hashrate and difficulty increases. If you pay a thousand or 2 dollars for something and don't do research beforehand it is your own fault for making a bad purchase.
It isn't up to them to find out if you can make a profit when you purchase something. That is your job.
That is why I have an L3+ and not a D3, though sometimes I wish I would have gone with my gut and got an S9.
There will most likely be people on eBay who will buy your unused D3 for a little more or at least the same you did. Do not hash with it a few days to 'try it out' and then try to sell it.