You neglect the part of the scheme above that's moronic because you spent tens of millions of dollars to attack a chain with less than that much immediate liquidity on any exchange. If you were to spend tens of millions of dollars making lots of ASICs, why not just mine with them like everyone who has made ASICs so far is doing?
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For instance, your net profit per day right now mining Bitcoins with 80 TH/s (enough to attack the network) is $530,445.73 (after power given a mildly inefficient ASIC). Why would anyone in their right mind perform a 51% attack when they're making that much per day off their hardware?
If someone has a net worth of 50 million to 100 million, then attacking Bitcoin is stupid! They can make much more mining!
That's not the person I am talking about.
If someone has a net worth of a billion and they can make a lot shorting the entire Bitcoin system, they might spend 50 million to enable this, or maybe a bank or government that doesn't care about making several million more a day when they can make more in fees for moving money around once Bitcoin is destroyed.
The 51% attack is a real viable issue and for 50 million you most likely could destroy all Litecoin and Bitcoin confidence. That's not a lot of money to destroy a billion dollar economy or a rising competitor.
The linear 51% attack is a expensive but viable attack vector.
Until there exist hundreds of thousands of ASIC run by good actors we are in a dangerous era of crypto-currency.
To put it in perspective, the profits of a large bank in one month could easily lay waste to Bitcoin, the profits of Apple in one day would be enough to build ASIC for both Litecoin and Bitcoin and erode all confidence.
Exponential attack vector for the network is required at some point, someone smart please figure it out.