Not true. There can be other blockchain(s) where incentive to secure the blockchain can be something other then monetary value of BTC. For instance people can be blackmailed to secure the blockchain or something valuable can be denied to them, like access to some service or goods. Those negative-utopia scenarios are not hard to think of. Secure the blockchain or there's no internet for you. Secure the blockchain with national cryptocurrency or there's no citizenship rights for you: no voting, no passport, etc. So blockchain technology is valuable without the BTC, just not (yet) usable as Bitcoin is.