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SHA1 is insecure because the SHA1 algorithm is insecure, not because 160bits isn't enough.
I would argue that 160-bits isn't enough for collision resistance. Assuming RIPEMD-160(SHA-256(msg)) has no flaws (i.e. is a random oracle), collisions can be generated in 2^80 queries (actually detecting these collisions requires some time-memory additional trade-offs). The Bitcoin network at the current hash rate performs roughly SHA-256 ~2^78 queries a day or 2^80 queries every four days. Without any break in RIPEMD-160(SHA-256(msg)) the US could build an ASIC datacenter and produce RIPEMD-160 collisions for a fraction of its yearly cryptologic budget.
The impact of collisions in RIPEMD-160(SHA-256(msg)) according to "On Bitcoin Security in the Presence of Broken Crypto Primitives"(
https://eprint.iacr.org/2016/167.pdf):
>Collisions are similar, though in this case
both public keys are under the adversary’s control, and
again the adversary does not have access to the private
keys. In both scenarios, there is a question of nonrepudiation
external to the protocol itself: by presenting
a second pre-image of a key used to sign a transaction, a
user/adversary can claim that his coins were stolen.
How would such an event effect the price of Bitcoin when headlines are "Bitcoin's Cryptography Broken"? How much money could someone make by playing the market in this way?
For both reasons of credibility and good engineering (safety margins) Bitcoin should strive to always use cryptography which is beyond reproach.