Yes, you are responsible for all the code you ship to your users. Not pinning dependencies is asking for trouble. It is literally, "download random code from the Internet and hope for the best."
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Code with publicly-known weaknesses poses exponentially more danger than code with unknown weaknesses.
It's like telling sysadmins to not waste time installing security patches because there are likely still vulnerabilities in the application. Great way to get n-day'd into a ransomware payment.