Linux, particularly the GNU/FSF types, tend to be more ideologically motivated, I find, and I think most of the hate against Free/Net/Open BSD is hate against the BSD license because it doesn’t fit into their framework of how the world should be. They’re the ones that are going to be on about “software freedom” and all that, rather than “this works, let’s use it.”
Case in point, I mentioned above that I actually paid money for a commercial X server about 11 years ago. If BSDi BSD/OS hadn’t been $1000, I’d probably have bought the “commercial” BSD, too. However, FreeBSD tended to get most of the worth while improvements rolled back from BSDi, and it only cost me like $30 to order it on CD-ROM (the dark days of dial-up and all that). My current company uses FreeBSD as the basis of our product to avoid GPL issues, as does Juniper and others. The FSF-types, of course, aren’t going to be down with that and look at it as “theft” (never mind the fact that I know my company, and possibly Juniper as well, have committers on the pay roll) or something.
I think it has to do with the fact that Linux is more readily obtained and there has been a concerted effort to recruits new users. Its sort of like the Mormon Unix, in a way. What this means in practicality is that there is a large portion of the user base that has the “zeal of the convert” — I’m not going to say that I didn’t feel that way when I was 12/13/14 years old and was first starting out, but it’s a real thing. As Theo once said, ‘bsd is for people who love unix; linux is for people who hate microsoft.’ That’s kind of a classic troll, but its kind of true, too, to an extent.
I think that the type of people who are into BSD are generally older, have more experience in the industry, and are less ideologically driven in their OS choice than say, high school kids who saw pretty screen shots carefully crafted to look like something out of ‘swordfish’ or ‘the matrix’ an want to be ‘l33t’. That’s not to say that there aren’t a lot of professional, neutral-minded Linux people, but then that’s going to be the difference between the RHEL/CentOS-type of users and say, Mint (which I’ve tried and used before and I don’t hate it, but let’s face it — we’re not putting that on a production server any time soon).
BSD and Linux have their places, as do Windows and MacOSX. I (obviously) prefer BSD to Linux (though I’ve worked as an admin on a CentOS farm before), and Mac to Windows (though I didn’t really have any problems with Vista 64 Ultimate as a desktop OS, just the command line was still for crap), but I can use the other and often do, and I’m at a point in my life where just getting the work done with the minimum headache is more important than what tool i use to get it done. From what I know of Linus, he seems to be of similar mind, too.