Certainly one can be a fan and critical. But an awful lot of the criticism coming from the boards lately has been borderline to blatantly insulting. That's less criticism than abuse.
To be fair though their are some fans of the company that can be just as bad. Constructive critcism or not your not allowed to say anything negative about the company. While I don't always agree with how some of the negative critism is said. I do understand. For the most part it's comes from frustration. If the community is asking for new material to be both balanced and worth taking for a player. We keep getting either options that are too strong. Or simply not worth taking. So far beyond a few exceptions. I have not used most if any of the new material in the later books.
Their errata process leaves much to be desired. So far I'm seeing nothing that changes my impression that they don't like martials. Or they go to far and the material joins my list of what I'm never ever going to take as a player. Or what truly is a problem simply gets ignored. Even when many people point it out to them.
I can blame people for leaving or being more vocal. I don't reward any company with praise when they keep making the same mistakes. I'm not the only one that feels that way I'm sure.