To start us off, let us look at this quote:
Opinion is ultimately determined by the feelings, and not by the intellect.I suppose for many reading this, on the surface there is nothing objectionable in this statement. If anything, it probably sounds fairly reasonable. After all, we have become so used to contrasting "opinion" with "knowledge" that the ideas embodied in this have almost become conventional wisdom.
However, the common practice of defining "opinion" as something of a synonym for "uneducated guess" or "personal bias" or some other sort of arbitrary belief, is itself incorrect. And many of our uses of "opinion" demonstrate this. For example, courts rely quite heavily on "expert opinion". Which should help to make it clear that "opinion" is not exactly what most of us think it is.
Opinion, properly defined, is, to put it simply, a decision reached without definitive evidence. And so, in some cases, it may very well be nothing but the expression of a personal bias or arbitrary decision. On the other hand, it may be a decision reached by examining a great body of evidence, and applying quite a bit of thought. Thus, an opinion may, in some cases, be quite easily dismissed, but in many others it is something we should take quite seriously.
Which makes me wonder why we have become so dismissive of opinions, treating them as having little more weight than personal tastes. As this quote demonstrates, it is not exactly a novel phenomenon, and yet there is little reason for it.
My personal theory, or opinion, if you will, is that it is based upon the same motives that inspire many to misunderstand the meaning of the word "theory", so they can dismiss anything from evolution to free market economics as "just a theory". If opinion means nothing more than an individual whim, then those who are scrupulous enough to distinguish their professional opinion from fact, in other words, the very experts to which we should listen, can be easily dismissed, as they are just expressing and opinion, just like anyone else. In other words, in any field where there is no absolute truth, which is most fields outside of mathematics and formal logic, the dismissal of opinion allows the field to remain wide open, since any opinion is as good as another.
Which is why I selected this seemingly innocuous quote. Because, trivial as it may seem, the readiness we show in dismissing "opinion" is a symptom of the modern tendency to dismiss expertise and empirical evidence when it does not suit one's beliefs. All of which makes it impossible to evaluate the various theories being put forth, and leave, for example, one's choice of economic theories, as nothing more than "a matter of opinion", by definition something entirely arbitrary. And that lack of any means to evaluate competing theories, that leaves us in a very dangerous situation.
NOTE: In the two essays which I wrote about Herbert Spencer's quotes, I must admit I am relying upon online quote sites for the texts. I read some of Spencer's works many years ago, but confess I do not recall enough to vouch for the validity of the quotes, nor whether they were removed from a context which might change their meaning. As they do sounds rather modern in their thinking, it is possible they were cherry picked by modern readers looking for support for some argument and thus may be misleadingly removed from a context which alters their sense. So, if I am wrong about how they should be read, please let me know.