I've changed my mind on the subject several times already, and at the moment I think, yes, their selling is the main cause of the bleeding market we see during the past three weeks. Bitcoin price had stabilized at around $6,400 and then, all of a sudden, exactly at the time when those guys began to struggle for buying more hashing power the price started to drop. It is hard for me to think of it as coincidence.
Firstly, you just blindly assume they have tons of coins to sell, which they might not at all have. Bitmain, Roger, CSW, and a bunch of other fools have done everything they could to unload as many of their BTC to preserve their 10-15-20% BCash pairings, which they failed to do because there just aren't enough coins to utilize.
The likely reason it happened afterwards could very well be an institution or even miners themselves cash out some of their holdings. The difficulty adjustment was around the corner, plus it was clear that Bitmain with its Antpool, BTC.com pools and ViaBTC pool would shift over hashrate to protect their own chain. Lower hashrate + lower difficulty adjustment = lower production cost.
Another reason why I want to think that the "hash warriors" have been causing the today's downfall, is because I want to stay optimistic and I want to believe that the market will start to recover when they will run out of their money. (can take up to 3 months counting from the beginning of the war, according to my estimations).
Not saying that my opinion is the right one though. This is just my current personal opinion, which is subject to change over time.
I'm sorry to say, but with what you just stated you invalidated everything you said regarding this subject.
The whole point is that these idiots are out for attention. They don't have hundreds of thousands of coins ready to be dumped. As I said above, they spent most of their BTC resources on having BCash be paired to Bitcoin as far as they can financially sustain it, and they failed.
I am very disappointed with how poor the 'hash war' actually was, because their big words didn't match their actions. Why? They don't have the financial resources to sustain it.