If this were just a good article about Mongo, sure, that's fair. But I don't think "fair" can be stretched all the way to "let's not be critical of biased comparisons simply because we expect the source to be biased."

Do you honestly expect a product or company blog to give an unbiased account of the product or company?

I don't always rely on people to be honest, but I do expect them to be honest.

Why does business have to be built on dishonesty?

Human nature.

People get burned when they assume honesty and find that counterparties are dishonest. It's harder to get burned if you go into business or other intellectual relationships without expecting honesty. And I think, push come to shove, many founders will do what is necessary (no matter how unscrupulous) to keep their startup alive or to ensure the big payday, even if it comes at the price of turning back on promises or contracts with customers

I recommend you read http://www.zerohedge.com/node/13972 (the Conflicts/"Full Disclosure" Policy for zerohedge.com) as I think it captures the point very well.

It's a very good way to bring trust to your brand. If you honestly say: "This is good with <product>, this is bad with <product>". If you do that enough, and isn't afraid to say that in <particular circumstance> a competitor's product is better, you might in time be seen as something more than a salesman.

tl;dr: never underestimate "reader's tacit or criminally negligent acquiescence."

'If you honestly say: "This is good with <product>, this is bad with <product>".'

In order to evaluate the veracity of the claim, you have to try the product. And if you have to pay money to try the product to verify the claim, then it's unclear as to how many people will actually bother to verify. If you price it high enough that the number of people is zero, then you could say whatever you want without others knowing if you are being honest.