Well, this is exactly what we are talking about in this topic: If it turns out that Bitcoin has a fatal or near-fatal flaw that makes it vulnerable to a particular kind of 51% attack, then its price will drop severely.
Maybe I went to low with the prices in my example, so to really underline the point, imagine instead that the cars cost $190k to make, and it turns out that their motors have a risk of exploding, or something like that.
If it turns out that there is an attack vector on Bitcoin where attackers can keep stealing money and profiting as long as its price doesn't crash, then Bitcoin will crash (i.e. unless the attack vector is mitigated). You have to agree with this, don't you?
(And if you do, then we don't really need to discuss this specific topic anymore in relation to the overall topic of this thread, even if we still disagree on some points: We could do that in another thread.)
lets get serious about your analogies
if cars cost right now $50k-$300k to build, due to underlying material cost
by having another car manufacturer join creates competition and takes away some material meaning the material cost increases
yep just the increase of hashrate alone due to ethereum users switching to mine bitcoin will cause the underlying cost value:premium to increase
this then makes the retail/dealer sell cars publicly for more
yes if there was a fatal flaw that explodes engines or makes miners defunct to cause hashrate to drop. then yes this can also cause the underlying value to drop and thus the market price to go down when the public stop demanding bitcoin
however a ethereum group cant change the network just by having control of blocks. they still have to obide by the design of the network, if they tried to design a new algo that had a flaw. they would just create a new altcoin. and it would be that altcoin that fails(explodes)
bitcoin has had 15 years of safety checks of the main safety features, heck even satoshi himself left a p2pk address with some bitcoin on it that is in a re-used address thus leaving some data leakage of keys. and no one has been able to steal satoshis coins from the known address he send coins to hal and sent coins back as change
so trying to imply that a ethereum group can steal other peoples coins is a sign you have not researched bitcoin nor its risk mitigations and instead you just want to keep dreaming scenarios hoping someone will kiss you and tell you ethereum will be king,. becasue you evade actually going deep into wanting to truly know about bitcoin security and features that protect it. you instead change your attack scenario to try to pretend there is another way to do it
you need to realise in the many many months pre-atack the ethereum group shift over to bitcoin they would work as honest miners whilst they wait for leadership announcement. and then even when ethereum leadership announce an attack date. the result would be that the attackers would be working on a blocklist that is not visible to the honest network for multiple blocks and is not guaranteed to take over the honest network and pursist
also the attempt to re-spend old confirmed funds would only be worthy if the value involved was significant, to which services would log which funds are being undone and mitigate the user re-spending those funds
there are many mitigating circumstances and features and economics at play, even things like a pool needs to have their block visible and unorphaned for 100blocks before they can spend the rewards. however the honest network can reject the malicious pools blocks by simply not accepting the blocks that dont have the previous hashID of the blockheight
EG
if malicious pool started attack at block 850,000 but only got to catch up at block 850,070 the block 850,071 from malicious pool wont have the 'previous hash id' of the honest networks 850,070