I don't follow him closely enough to know why a lot of people seem to hate him. What about the 9-to-5 mac guy? Do people hate everyone not macrumors, or just him specifically?
A lot of people are jaded due to the nature of Apple rumors in general. There are a lot of "sources" out there that often report unsubstantiated (see: fabricated) reports for the sake of page views and ad revenue.
However, there are a decent number of journalists that rarely report garbage and are quick to point out the difference between their opinion and something that they heard from a source they trust.
John Gruber in particular has a signal phrase that he uses when he's reporting something that a source within Apple has told him - "A little birdy told me <insert information here>". If you don't see that in the post, then there's a good chance that he's stating an opinion or joking.
The problem is that the media tends to ignore these cues and report everything as if it is confirmed. In doing so, they do a disservice to their readers and to people like John.
All that said, today's post by John is him clearly mixing it up a bit and baiting news outlets based on the earlier reports issued on what was clearly a joke. He has made no secret of the fact that he is frustrated by the rumor mill culture of reporting first and verifying later. This is essentially him playing digital chicken with them.
Jim Dalrymple, Mark Gurman, and the Walt Mossberg clan over at re/code (formerly of WSJ) are all extremely reliable sources.
