Your difficulty is that you need an elevator pitch.
If you're unfamiliar with the term, an "elevator pitch" is a super-brief description of your book - basically, how you'd pitch it to somebody sharing an elevator with you. A line, two - no more. This level of succinctness is crucial, because from most potential buyers - both publishers and, eventually, readers - that's pretty much all you're going to get to catch their attention.
This makes marketing anthologies (of any kind - fiction, nonfiction, opinion, whatnot) extra-difficult - because you need to bundle a bunch of different, unrelated pieces into a single quick pitch. Consider your own reaction, if you were offered a book like you're describing. If somebody (say, other than a personal acquaintance whose opinion you trust) were to say, "Hey, you should totally try this book! It's got a whole bunch of essays on a whole bunch of topics! Yes, just like on lots of places on the internet - but this guy's really good and his ideas are really interesting!". Would you be excited by that intro? Would you believe the last part? Would you pay money for that? Or would you figure you could get the same in a hundred magazines and blogs? That's the problem you need to overcome - once you've got a pitch, your work will stand or fall on its own merits.
What's a good unifying pitch for my collection?
Common was to unify your pitch include:
- Focus on a specific topic. If you can focus on a single issue, the book becomes much easier to describe and to market. If you're after publication, you can deliberately target a topic. The topic also doesn't need to be entirely expected or straightforward - if you've got something clever or unusual, or something that stretches a definition in a way people will enjoy, that's great too.
- Focus on your unique style and character. Then that becomes the draw. "A Zen Master takes on everything from Piracy to Scientology!", "Delightfully tongue-in-cheek, Things White People Like mocks every staple of everyday life!" etc. etc.
- Focus on a consistent approach. Popular science books like Freakonomics or A Mathematician Reads the Newspaper cover a huge range of different topics, but they're all an attempt to examine a variety of issues in pretty much the same way. Similarly, if you've got a core insight you apply over and over, or a regular system by which you ferret out the basis for your controversial opinions, then that approach might be the core of your book.
- Have an existing following. Then the pitch is really easy - "read the exciting insights of [semicelebrity X]!". Nice work if you can get it.
What other options do I have?
It sounds, from your question, as though you're having a tough time finding a unifying concept. That's perfectly reasonable (albeit, of course, less fortunate than the alternative). In that case, your pieces might really be better off as standalones. If you come to this conclusion, you have a few worthwhile avenues to consider:
- Sell your pieces to professional publications. This is the single-piece equivalent of publishing a book. It gets your name out, it gets you paid, it brings you contacts, it establishes reputation in the field. You can even spread out into several directions and different publications at once, which is really rather nice. Don't forget to consider respectable, popular online venues - writing a guest post for a really popular blog gets you a lot of readers, at least briefly.
- Blog. It's tough to get a following, but good content will generally find an audience. A decent blog readership is often acheiveable - and could even be the basis for the "have an existing following" option for some later project.
- Self-publish as an eBook:
- As a collection - This is straightforward, and gives you the self-publishing version of what you wanted for traditional publishing. But, you'll run into the same problems selling this that you would with writing a pitch to begin with.
- As individual ebooks - this might be a great solution if you really think you've got marketable content. Split up into a bunch of tiny ebooks; sell 'em cheap. This lets you pitch every single one of your essays independently; each individual pitch will be much easier; each individual ebook will be cheap (and hence pretty attractive to newcomers). You might even distribute some free, as a sample that'll help draw more readers to your ideas and your writing.
- Both - lots of itty-bitty little ebooks, and one "big" one collecting them all. The small ones are great as above, but they also direct readers towards the big collection. This is no guarantee that the big collection will sell nicely, but this is literally no additional risk (and very little additional effort) beyond what you've got for the individual ebooks. So, yay!