Well, I've been going back and forth with his teacher about this a bit.
His side of the story is that he's trying to get the students interested in the world around them, and he's using current events as one way to do this. He told me he does try to tell them when something is his opinion, and tells them when there is conflicting viewpoints on a subject. He said "my usual end retort is, "What do you think? Find out and make up your own mind."
I'm sort of OK with that. The problem, as I pointed out to him is that these 10 year olds do not yet have the research skills to find out this information, and most of them (my son included -- he's particularly gullible (it's a family trait)) don't have the cognitive development to question authorities. I pointedly asked him if he was teaching the students the research skills necessary, and he sort of hedged. THAT bothers me. They are going to do an expository report as their next writing assignment. But he didn't say that they're going to look for conflicting viewpoints. He openly acknowledged that the range of skills in the class is so broad that they probably don't have the cognitive development (seriously they have kids who arrived two months ago in the US and are working at a Kindergarten level to my son, who's pretty much at the top (and while he's bright, he's not brilliant)).
I'm particularly bothered because the demographics of the school are such that most children there don't have access to information to "find out" for themselves. When ds came home spouting garbage about there being pyramids on Mars, I made him search the NASA website. We talked about how the higher resolution photos have shown that things were originally thought to be one thing (like the 'face' on Mars) turned out to be natural land formations. Most kids in our school don't have computers at home (really, we're a very high poverty school with a very high percentage of non-English speaking parents with low education). A lot of kids don't have parents who know where to direct them because the parents themselves have weak education backgrounds. And none of them have the resources to rebut (within 24 hours, like I do) the claim that "Cairo" means "Mars", and isn't it weird that Cairo is in Egypt where the pyramids are, and people think they've found pyramids on Mars, especially since it's not clear how the Egyptians could have built the pyramids with the technology of the time?
All I really achieved was ticking my son off because I'm "making all this stuff not cool anymore". 
I don't mind the teacher raising controversial topics, but I do mind that the teacher's saying these sorts of things with students with weak skills (ds' class seems to be particularly weak this year, which I'm kind of grumpy about for another reason), while at the same time they don't have time in their day to get the skills they need to do the research.
I did get his attention, at least, and made him think. I don't think he's had a parent in long time who's questioned him in terms of the kids' cognitive development. I think he doesn't know what to do with me!
(And for those that are interested: Cairo, in Egyptian Arabic isn't Cairo but "'alqaahira', which means 'the conqueror', and the root /q-h-r/ means 'to subject, to subjugate, conquer, vanquish, defeat, subdue, overwhelm, force, compel, coerce' etc." (quoting my Arabic speaking linguist colleague). Since Mars is the "god of war" I suppose there could be a connection, but it's pretty tenuous. Furthermore, most people refer to Cairo as "misr" which technically means Egypt, but is used in the same sense that people say "Washington declared today..." for the US. They add a qualifier (Misr the capital) if they need to specify the city. Add to that the fact that Cairo was founded long after the pyramids were constructed, and that there are enough workers villages around the pyramids to suggest that a gazillion workers worked on the pyramids -- none of this "woo woo" stuff is true.)
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