For the sake of clarity, let us consider the two widely known, nonsensical scenarios: The first is one that many scientists charge ‘idealist’ philosophers with, although no thinker beyond the dorm room bong level holds this view: All is just a dream and there is no physical world. The second nonsensical scenario is that a physical world “really exists independently out there” and it happens to be the case that consciousness arises in it although it could have conceivably been otherwise, a physical universe just being without consciousness.
The first scenario is easiest dealt with. There cannot be the consistent opinion of that it all “only seems”, because the word “seems” means that something is in some sense illusionary or deceptive. Something can only be deceptive in as far as it differs from reality. Assuming no “reality”, the only deceptive illusion left possible is that it seems that there is something “behind” that seeming, however, there is not. But then, that seeming is thereby reality, or anyway the last level we still label as “existent” thereby is.
The stories we experience are constrained in some way, and that is what “physics” refers to. It especially refers to whatever is relatively only indirectly correlated with observers, for example inter-subjective aspects such as planet earth, which has been around before us and thus “did not need us”, for example in a description where “flow of time” is held to be somehow “absolute”. Those who understand this never say that there “is no physics” or that it is “just a dream”. A dream is a dream and physics is physics. That the physical is “logical fiction” does not mean that it is “merely” fiction. The implied physical is as real as necessary, as real as you can get.
“It all only seems” expresses a feeling, a suspicion of absence of some more solid, reliable base that one had hoped for(!). Idealism is more worried and critical, while realism is an optimistic way of painting with language. [There is in general no more behind the controversy, if not one focuses on narrow definitions (like “realism” as “counterfactual definiteness” in quantum physics). Structural realists and transcendental idealists by now embrace each other as equals and go on to create poetry about the difference nevertheless, to survive and for the fun of it.]
The second scenario is difficult to reject in front of scientifically educated folk, because they tacitly believe in that scenario as if it obviously makes sense, all difficulties surely being temporary. It does not help to explain to them that the language used, like “existence”, has no proper meaning without being somewhere anchored in “existing for me”. The naïve physicalist belief, even where it is denied, is so strong today, feels so obvious, and the certainty about that everybody reasonable agrees is so confident, they refuse the demand for proper language as a rhetoric trick, as a sophisticating that should just shut up and accept the facts, period. Notice that the first scenario was just refused by demanding proper language, because that can work with those who hold such views, as they are somewhat less naïve, less religious than science fans.
To refuse the naïve physicalist scenario in front of the sciency in-crowd, it is perhaps best to first explain that patterns cannot be conscious, that there are no conscious physical states without processes over time (1), then pointing out that there are no conscious processes in a non-quantum description either, because processes are then just patterns in space-time, doing no more than a static pattern on a chess board (2), and then finally explaining that a naïve physicalist interpretation of quantum mechanics cannot help either, because it turns all space-time patterns into their correlated mess of all possible patterns, but all possible patterns are no particular pattern at all (3).
The first point is about that all patterns can be found in any rock. If conscious experiences were ‘instantiated’ by excitation patterns, any state of mind could be found almost anywhere – all you needed to do to prove the presence of any particular one is to employ a suitable mapping. The third point is similar to the first in that we arrived at there being something inside of which there are all “possible” patterns, including our witnessing unicorns dancing on rainbows.
I will not pursue this 1-2-3 argument in further detail here because it is boring and anyway just a fashionable version. Wise people knew the core of the argument 2000 or many more years ago, like Parmenides. That a pattern over time is just a pattern, or that all possibilities are all possibilities without alternative, such tautologies are self-evident and gain nothing from relativity theory or quantum speak.
The third point may likely be countered by some mysticism such as “what about real quantum mechanics with real time”. Here is where many hold on in desperation to physicalist gut feelings without ever understanding the trivial core argument: The very modification you need to add to the naïve physicalist patterns that supposedly instantiate experience is the very fact of that the “alive” patterns are distinguished from all the many more plentiful alternative ones by the logical consistency of the patterns as experienced “from the inside”. Insisting on that the patterns also “really independently exist out there” adds nothing, regardless whether you call the pattern containing thingy “rock” or “quantum universe”.
An alternative feeling to that of naïve physicalist realism, one just somewhat less fundamentally meaningless, is that the whole is possible precisely because it does not need to “really exist out there” in a way that would satisfy a naïve physicalist. If ‘Totality writ large’ needed to “really exist out there” in order for us to experience our lives, we could not be, because there is no “out there” outside of totality in which it could “really exist”. This is part of the answer to “Why is there anything?” – it is not just so that the question has no answer of the desired sort. The answer to many naïve versions of "Why is there anything?" is simple: There isn’t anything in the way you feel it must be!
There is sunshine in physicalist ‘good old realism’, a hope. As long as there is a necessary substrate that is physically restricted, not every evil is possible. However, if it is all just stories, anything seems possible; all cruelty whatsoever would be real. Quantum mechanics is a bridge, because it has one foot in “the physical” but the other in that it all “only seems”. Unsurprisingly, it indeed threatens that “anything is possible”. Especially the naïve realist therefore fears quantum mechanics, but quantum mechanics associates with cruel totality of fecundity for anybody able to tune into such.