While there are certain ethics all writers who give voice to words (be they blogger or professional journalist) should follow regarding plagiarism, slander and truthfulness, there is a distinct difference in the realm of blogging verses being a professional journalist.
Media sourcing tends to put a professional journalist in front of a larger audience where he or she would need to give considerable thought and attention to the news and information being shared. The repercussions of a professional journalist lack of ethics has severe consequences for his or her career and creditable believability.
A bloggers ability to prejudice, incite or hurt a person due to differences of opinion or belief (when blogging) while damaging, would be limited to that individuals followers and small population of word of mouth exposure. Yes, they can be held accountable for slanderous comments as seen in a recent situation regarding inappropriate comments left on Twitter. Still a bloggers exposure to a wider audience pales in comparison to a professional journalist.
A professional journalist is out in the public eye, having the ability to sway the world. His or her article, news piece, or TV appearance has a greater chance of being picked up by several syndicated newspapers, magazines and news stations. A bloggers audience tends to be far smaller.
Regarding sources, a blogger doesn't necessarily need to be tied to the same code of ethics as a professional journalist. A journalist has his reputation at stake, his credibility, (not that a blogger doesn't) but as a professional he or she would want to follow the rules of ethics regarding truth, protection of source and presenting factual information. A professional journalist would never give way to careless assumption, which could later bite them in the proverbial butt, ending their professional career. A blogger usually blogs for self, so he or she wouldn't worry so much about reputation.
A blogger isn't necessarily a professional blogger. He or she isn't, in most cases, affiliated with some major writing source. This doesn't mean they can't cause damage by not considering what they blog about and can't be held accountable for misconduct. A professional takes sort of an oath regarding their work and a blogger doesn't, so how could the same moral ethics apply?
While bloggers and professional journalist share a commonality of writing. A blogger will usually touch on whatever affects them personally. Often giving more of a personal view on matters. A professional journalist is usually assigned a specific job and will need to approach his or her assignment without bias. Two different approaches, which shouldn't be bound by the same codes of writing ethics.
What it comes down to in the matter of ethics, is whether or not the blogger or professional journalist are bound by certain laws and principles. When a professional steps out into the lime light they are inviting public opinion be it good or bad. Largely the reaction of their audience depends upon the way they go about presenting their information. So by all means they would need to be ethically correct. There is definitely more at stake with a professional journalist than there is with a blogger.