Sure, there are such conspiracy theories, and will be more, and indeed it’s hard to sell collective responsibility. This is not new, for example I recall plenty of rubbish about chemtrails in the 1990s. Whether it matters depends if it impedes agency of too many people. Regarding collective responsibility, people might feel more agency, if they felt more equity. In this case first acknowledge that there is a real global elite (anti-tropes can become tropes…) who jet around for conferences and holidays who do contribute a lot more than most people to the climate problem - plenty of data now about the 1% etc, on the other hand that can also show that focusing only on them alone wouldn’t be sufficient, our everyday lives count.
It also helps for agency if proposed ‘solutions’ are within the resources / skill-set of DIY types, not just expensive high-tech for big-organisations. Could ‘preppers’ convert into ecologists - it’s not so far removed…?