Should you self-publish a book? There is no easy answer to that. It depends on many things.
Why Did You Write the Book?
If you wrote your book because you need publishing experience for your academic career, it is not good to self-publish. If you hope to get your book in university libraries, it is not good to self-publish.
But what if you just had a story (fiction or non-fiction) that you wanted to tell? What if you just enjoy writing and finishing a book is the motivation you need? What if you are writing the book for yourself? In these cases, self-publishing may be the way to go.
Disadvantages of Self-Publishing
There is still a stigma to self-publishing. Anyone can self-publish and there is absolutely no quality control. Unless you already have a reputation, there is no reason for people to believe your writing is any good.
Being published by a recognized publisher looks much better on a resume than a list of self-published books.
Publishers will push you to write better. If you self-publish, you have the final say and you can set the standard as low as you want. Publishers will make you a better writer.
Advantages of Self-Publishing
The purpose of publishers is to make money and not to fulfill your dream. If you desire to publish a book, it is within your power to make that come true.
You take control of the marketing of your own book. There was a time when that was a disadvantage but with social media and blogging, an author can do a good job of marketing their own book and for very little money.
There has never been a better time to self-publish. It is easier and cheaper to self-publish now than at any time in the past. There are new tools available all the time.
The quality level is coming up. While there are still books being self-published that will never sell a copy, there is a new crop of talented authors who are taking advantage of self-publishing opportunities. The bar is slowly being raised.
Should You Self-Publish?
So is self-publishing a bad idea? Self-publishing by itself is not a bad idea. Although there may be circumstances where finding a recognized publisher is a much better idea, there are other times where self-publishing is the way to go.
I have had a book published by a publisher and it was a great experience. I have self-published and that has also been a great experience. I recommend both routes.
My final piece of advice would be to not dismiss self-publishing but also to not rush in and self-publish everything you have ever written.