... I already explained that we do not lose fifty percent of our security at the halving, since the exchange rate also effects this dynamic ...
Not really. This year, we are paying roughly 10% of Bitcoin's total value, or what people here call "market cap," to secure it. In other words, we are currently spending roughly a dime to store (secure) a dollar for a year.
After the halvening, we will be paying only a nickel.
It doesn't matter how much a dollar is worth, the ratio remains the same.
Same for efficiency/cost of mining gear.
What matter is how much a Bitcoin is worth compared to fiat, since if the market capitalization of Bitcoin increases, the block reward will be worth more in terms of fiat value and real world purchasing power. This would stimulate increased mining since there will be profit to be made, since miners costs are still predominately in Fiat and it is the purchasing power of those Bitcoins that really matters not the amount of Bitcoins that are made. This is why the ratio does not stay the same, if the market cap of Bitcoins doubles so does the amount payed for security, these two things are explicitly linked.
But it doesn't matter. A safe that's "just good enough" to secure 10 dollars is probably not good enough to secure a billion, agree?
The attacker doesn't want to break Bitcoin to prove a point, the amount he's willing to spend on the attack is directly proportional to the potential reward. So if it costs him a buck ten to steal a dollar now, after the halving it will cost him 55 cents.
Bitcoin price in fiat doesn't play into this, because it affects both the cost of the attack and the reward equally.
Tell me if I'm being unclear.
The cost of the attack is measured in fiat. Since to buy and setup more then fifty one percent of the hashpower would cost more then two hundred and sixty million dollars (just ran a rudimentary calculation). If the price of Bitcoin however went up, it would in effect mean that the Bitcoin protocol is paying more for its security in terms of fiat or real world purchasing power. This would incentivize more miners to come into the ecosystem thereby increasing its security. Therefore it can be argued if the price of Bitcoin doubles that the security of Bitcoin would also double meaning that it would cost twice as much to attack the network, in this case for example it would cost more then five hundred and twenty million dollars, and this is just for the setup costs, not including maintenance or even electricity costs which would over the long term might even cost more then the machines themselves.
Pardon me if I don't trust your back of the hand calculations, your assumptions and narrow minded view that ignores the possibility that a miner or hacked mining pool/pools might desire to attack the network just to short the price and turn a quick buck, is absurd. An attacker my already have a large stockpile of bitcoins, perhaps confiscated in a drug bust but who are you to set the limits on a theoretical attacker and their potential resources?
This attack vector already exists today, and increasing the blocksize does not change this. I am not overly concerned with the possibility of fifty one percent attacks. The game theory of Bitcoin pretty much prevents this from becoming a serous threat in the first place. In the case of a government attacking Bitcoin, our best defense is to grow as quickly as possibly so that it makes this type of attack much more difficult both politically and financially.
politically yes but financially I absolutely disagree. Larger blocks at this time could lead to massive spam attacks leading to massive and prohibitively demanding bandwidth requirements on our weakest nodes leading to first torrents of orphaned blocks then whole orphaned chains then hard forks left and right leading to chaos.
You are saying that if we increase the blocksize at all it would lead to the very destruction of Bitcoin? This is such fear mongering it really is, an increase to two megabyte or even eight megabyte would not lead to the catastrophic scenario that you are describing.
First of all larger blocks would allow the Bitcoin network to become much more resistant to spam attacks, since it would make effectively overloading the network much more expensive. After all for the vast majority of Bitcoins history this blocksize limit has existed far below the actual transaction volume, these spam attacks have only become an issue recently since we are approaching this blocksize limit. Making it rather easy and cheap to overload the network, this would not be as easy or as cheap with an increased blocksize.
There are many prominent engineers and coders that think it will be fine to increase the blocksize, and that this was always the plan for Bitcoin. If it really is this obvious that any increase in the blocksize would destroy Bitcoin, why are all these good people like Gavin Andresen saying that this would not be a problem? Furthermore what is so special about one megabyte, it seems rather arbitrary to me, earlier in Bitcoins history it had a thirty two megabyte limit, this also did not lead to its destruction, or chaos and hard forks left and right as you describe. Bitcoin will do just fine, I think we should continue with the experiment and let it runs its course, not stop it in its tracks before it has even had a chance to prove itself.