if the code is not released by "team core"(centralised) then its not bitcoin
by even having the mindset that anything not core should be treated as an attack and as a future altcoin if it goes against the blockstream roadmap is an admission that bitcoin core is not decentralised.
this mindset is not necessarily bad.
obviously not everyone is knowledgeable enough to know who is right and what solution is best so they have to follow someone and trust their plans. and who better than the team that has been developing bitcoin for years.
but also it is not good if everyone starts having this mindset and gives up educating themselves and thinking. and it is even worse when they try to shove it down other's throats. the second part is unfortunately what has been happening mainly last year.
i wouldn't go as far as calling it not-decentralized since this is mainly in social media like reddit for instance but this mindset should die if we want to see a better bitcoin. which means for example when you ask others why are you rejecting SegWit2x their answer should either be "i am not knowledgeable enough to answer" or they should give a logical technical answer.
i used this specific example because every time i read an argument about SegWit2x the heart of it all was "because core rejected it".