Market goes down: "grr... this is just a dastardly ploy to further wealth inequality because the rich can buy stuff on the cheap!"
Market goes up: "grr... this is just a dastardly ploy to further wealth inequality because stocks are overwhelmingly held by the rich!"
Whereas for regular people, an upswing means nothing, whereas a downswing means job loss, mortgage rate hikes, etc.
And poor can also capitalize on the up swings.
The difference is not so much in access to markets, but in who plays them better.
There are also major omissions like the fact that mortgage rates are often fixed (poor are protected), but margin rates are generally not (rich get hurt).
The fixed rate payer/receiver is protected but they typically pay for that protection.
You scoff at their representation of the problem probably because you think they are blaming everyone else but themselves, but objectively speaking, they are making an observation that would hold if one were, in fact, observing a fundamentally rigged system architecture. If you break down the principles around how the system works, it's an inevitable conclusion buying power centralizes, the people it centralizes in gain influence over the optimization function, they optimize it toward greater value centralization, and away from other actor's capacity to exercise agency and survive. Stable feedback loop established, checkmate in 5 (whatever units it takes five of to hit your personal definition of an unacceptable degree of centralization.
Important thing to also note, is that even if your sympathies are vested with the people the power is centralizing in, you're threatened by the increased level of conspicuousness and undeniability to everyone else. If the odds of someone coming after you significantly increases after your first 1-10 million dollars say; getting you 1 possible attempt on your safety to foil every 5 years, but every billion gets you an attempt every couple weeks; is it really still worth it? There's a lot of "Them" and "They" only have to succeed once. It behooves one to acknowledge that those dollars are perhaps better distributed to the point of raising everyone else up so as not to make yourself such a conspicuous target.
Food for thought.
For example, pump and dump schemes have both an up part and a down part. Not hard to understand things can be manipulated in either direction to benefit a specific group.
The pump and dump analogy doesn't really work because the crash associated with the "dump" isn't something that the organizer wants, nor do they benefit from the crash. It's just an unfortunate side effect from them cashing out and the truth catching up to them. Meanwhile the OP argues the opposite, claiming that companies knowingly made bad loans to create a crash, which implies more nefarious behavior than the standard explanation of bubbles caused by irrational exuberance. The latter is a conjecture that's not supported by any empirical evidence or even anecdotes.
Easy.