While I agree completely with your conclusion that mainstream media has thoroughly discredited itself in recent years, I don't feel masking likely-biased source

While I agree completely with your conclusion that mainstream media has thoroughly discredited itself in recent years, I don't feel masking likely-biased sources behind "anonymous" attribution is the biggest part of the problem. I do agree it's definitely been abused many times though. The even bigger problems are publication bias and source selection bias. These are far less visible because massive amounts of severe bias is accomplished by simply not running stories and it's easy to mask this bias internally because editorial decisions about newsworthiness and public interest are always subjective judgement calls the public doesn't hear about. In other cases, when editors feel the 'balance' element of an issue story they care about is a little "too balanced" they ask reporters to 'beef up' sources on one side and can also cut-down opposing view sentences for "space reasons". This is as easy as ensuring a 20 paragraph story gets assigned a 16 paragraph slot in the layout process, while ensuring the nettlesome "oppo" views are deprioritized to the last four paragraphs in the (supposedly) separate editing process. It's surprisingly easy to spot this. Just look for articles where you actually aren't sure which side the writers and/or editors lean toward. One would assume in a fair distribution there should be some noticeable number of these, yet it virtually never happens (and this is equally true from both right and left leaning media outlets). It turns out that it's very difficult for biased editors to sufficiently mask their bias, even when they're trying to appear unbiased.