I'm pretty confident that there's important stuff out there on Cascadia I haven't read, so I don't want to ascribe these to everything, but most of the stuff I have read suffers from some combination of the following:

1) Nationalism lite. This advocates for independence and sovereignty based on a claim of cultural similarity throughout the region, and lack of quality representation in distant out-of-touch legislatures. Both of these points are true to some extent, but are not really a compelling justification for an independence movement.

2) Vehicle for pet political ideology. A lot of people just use Cascadia as an empty vessel into which to pour their pre-packaged political fantasies, like anarchism, socialism, social democracy, libertarianism, or even national socialism. Some of these are clearly far more desirable than others, but they usually fail to justify why Cascadia should be the vehicle for their particular political experiment.

3) Environmentalist escapism (or perhaps escapist environmentalism). There are a few different ways to do environmentalism. The most common way is not at all, followed by half-assed. But there are two further ways. What I would consider the productive way is to approach society and the environment as systems which are integrated with and dependent on each other, and focus on building systems that allow for stakeholder-based sustainable management of ecosystems. However, the philosophy that a lot of environmentalists implicitly follow is that humanity is the adversary of nature (a recent historical truth), and that the appropriate solution is to segregate the two (as if that is possible), with humans into cities, and the countryside left to wilderness. Some of these environmentalists see Cascadia as a suitable vehicle for achieving this, since it would allow liberal urbanites to exercise political power over rural people who currently depend more directly on natural resources (including many of the Native peoples whose cause these environmentalists typically claim to champion). This is petty imperialism.

4) Absolutely nothing to say. A lot of time I'll read something and it will just be some feelgood stories about Cascadia without any sort of reasoned argument for why I should care.