(I previously posted this as an answer to this question, but Hamlet wanted to focus on actual textual analysis rather than discussing the intent issue, so I've separated this out into a new Q&A)
It's easy, even for people familiar with literary analysis, to conflate asking "Did the author mean this?" with "Does the work mean this?".
As you'd expect with an issue like this, there's no objectively true answer about who's correct here—asking if the author is right doesn't make a lot of sense, because there's no scale to measure right against. Instead, I'll introduce some of the common schools of thought on the issue of authorial intent (how you should interpret what the author wanted to say).
Some people would argue that the author—the person who created and crafted the piece of literature—is the one who knows most intimately what they intended to convey through their work. This view was favoured by the majority of literature critics until around the 20th century, when New Criticism and the intentional fallacy became more accepted.
Biographical criticism is one of the schools of literature which favours the author's intent and meaning as opposed to examining the text alone:
Biographical criticism is a form of Literary criticism which analyzes a writer's biography to show the relationship between the author's life and their works of literature. Biographical criticism is often associated with Historical-Biographical criticism, a critical method that "sees a literary work chiefly, if not exclusively, as a reflection of its author's life and times".
This longstanding critical method dates back at least to the Renaissance period, and was employed extensively by Samuel Johnson in his Lives of the Poets (1779–81).
By using context of the author's life, views and experiences, biographical criticism tries to uncover meaning through what the author may have intended to convey. Historically, this tended to be applied rather literally—the author's word was taken to be generally true without debate. This is not necessarily true in more modern analysis, though, where a balance is achieved between accepting the author's word and the other factors.
New Criticism is the form of literary criticism that comes to mind when considering the text as the primary source of meaning. New Criticism emphasises close reading (for context, see 'What is close reading?'), and tries to find meaning through the author's choice of words rather than their experiences and historical context.
It is debated whether New Criticism's method of almost entirely excluding historical context is effective. In The New Criticism: Pro and Contra, René Wellek outlines the major issues with New Criticism:
Four accusations are made more frequently. First, the New Criticism is an "esoteric aestheticism," a revival of art for art's sake, uninterested in the human meaning, the social function and effect of literature. [...] Second, the New Criticism, we are told, is unhistorical. It isolates the work of art from its past and its context. Third, the New Criticism is supposed to aim at making criticism scientific, or at least "bringing literary study to a condition rivaling that of science" [...]. Finally the New Criticism is being dismissed as a mere pedagogical device, a version of the French explication de texte, useful at most for American college students who must learn to read and to read poetry in particular.
It is worth noting, for context, that René Wellek was not criticising New Criticism himself—he was merely outlining the common flaws pointed out by others.
There is another prominent group of literature critics who eschew both of the above approaches, instead favouring you as the main decider of a piece's meaning—reader-response criticism.
What reader-response criticism tries to say is that a piece of work does not have one objective meaning that can be determined through careful analysis. The linked Wikipedia article phrases it well:
Reader-response theory recognizes the reader as an active agent who imparts "real existence" to the work and completes its meaning through interpretation. Reader-response criticism argues that literature should be viewed as a performing art in which each reader creates their own, possibly unique, text-related performance. It stands in total opposition to the theories of formalism and the New Criticism, in which the reader's role in re-creating literary works is ignored.
While writing this, I've reflected on the issue a little, and reader-response criticism starts to make a lot of sense. Critics in the past have read pieces and tried to find a way to interpret works and find meaning, as if it is an inherent property of a work, but, as shown by the many schools of literary criticism, each reader does find a different meaning.
Notice that I've written this without any reference at all to any specific book (like Fahrenheit 451, as I stated in the question). That's because I'm almost certain you would be able to switch the book title and have the exact same argument without gaining any real knowledge—any answer will either have to interpret Fahrenheit 451 from each possible view point, or simply state one opinion. Instead, I hope that I've started to share the tools to find out the answer on your own, or at least recognise how many literature critics would approach the problem.
In brief answer to the specific question: "Is Bradbury right?"—it depends who you ask, and what they think about literary criticism. A biographical critic would say "yes, of course he's right—he wrote the book!"; a New Critic would ask for the textual evidence to prove it and reader-response critic would ask what you believed the text meant!
When trying to prove if your conjecture is 'right' (if such a statement makes sense), you should consider how you want to prove it—close reading and analysis of text is often quite sound proof, but you may miss some of the context and nuance without considering the author's life and context. For example, in Of Mice and Men, racism is a major theme, but by not knowing the context of the novel in 1930s America, the meaning is very much lost.
In works of fantasy or science fiction where there is little historical context, close reading or reader-response may be a better choice, because historical context may be less clear, and possibly harder to justify than in a work that is clearly set in a historical period. Nevertheless, as Hamlet points out, fantasy and sci-fi works do tend to have some link to reality, so dismissing the point completely (as I had originally done) is probably not valid.
You can analyse literature from many different perspectives, but the predominant methods are author intention, text meaning and reader interpretation.
Confusing intention, meaning and interpretation can cause many issues when analysing texts, and, as pedantic as it may be, framing a question in a different way can drastically change its answer.
Asking who's 'right' or 'wrong' doesn't make a lot of sense in subjective analysis of literature—ask whether something can be 'proved' or 'disproved' instead for best results!