You are not breaking any laws as a reader if you read something for free online. If the book is pricey and not in the public domain, however, the person who placed it online is very likely violating copyright rules. Whether you favor copyright rules as a reader or not, they are in place to safeguard the author’s rights, not restrict anybody (or whoever owns the rights to that book at that time). Writers should get a portion of the proceeds from their intellectual property. If it gets given away for free, that’s money out of the writer’s pocket, in a sense. There are legitimate sites that offer free book deals; these happen with cooperation from the copyright holder. In those instances, there’s no problem.