It's only partly because it would interfer with my own writing, but the fact is, I'd be a really tough reviewer. On my Goodreads account, I have 11 reviews--so few because it takes time to write exactly what I want to say, or I feel foolish reviewing classics and bestsellers. For books that are popular but I don't share the popular view, I have less of a problem. However, I only bother when I feel passionately that the book isn't as great as proclaimed. Then I'm reaching out to others who, I'm sure, wonder if they're the only ones not loving this obviously "perfect" book.
I am a HUGE supporter of Indie authors but I am more tolerant as a reader than a reviewer. If I am critical of the craftmanship, my intention isn't to say, "I'm right, you're wrong" but to contribute to the dialogue. Unfortunately, opinions are often highly emotionally charged. Ultimately, the most important thing to me is that a reader enjoys a book. Maybe I can't understand why they are so enthusiastic (and I'm not talking about paid reviews). Just because I believe a novel is merely a good draft doesn't mean that the enjoyment of others is, somehow, lessened. But I don't want to cheapen my reviews to pure support, either.
This is why I admire reviewers so much--the ones who do this regularly and aren't just fans of an author. At this moment, I'm sluggishly reading a book that has received 4 or 5 stars from 68% of readers. While they gush, I see so many issues with character development, structure, and failed opportunities that I must conclude this was rushed to be released. Its potential is a distraction to me and so I read out of loyalty, not enjoyment.
I remind myself, often, that I've LOVED books that weren't perfect examples of craftsmanship. I've endured peers who derided a beloved book because of textbook issues I didn't notice, too transported was I to bother with such trifles. I'd think to myself, "Snob" and continued loving the books (think Harry Potter).
What I've discovered is that there are readers, reviewers, and practioners.
Readers of the craft aren't wrong. If they love a book, that's simply fact.
Reviewers of the craft, ideally, see more than just their personal pleasure.
Practitioners of the craft demand more from an author than just pleasure. They demand art.
Each of these are important and should be celebrated. It's why I don't fear a good, rigourous review. I, personally, would rather improve. But I hope no author ever dismisses a connection with a reader. That is magic, no matter how well the spell is spun.