I suspect that many of the negative influences of TV on kids that we all know for a fact happen are actually a combination of rose-tinted spectacles and the shockingly bad reporting of academic studies* that we're inflicted with in this country.
I have a slight knowledge of it having read some of the primary academic literature, and there is a lot of evidence that tons and tons of TV might be bad for people, and that it isn't so good for under 2s. Some kids really are watching quite a lot of TV mind, so the worst cases in the studies really are watching a lot.
It is quite nuanced, but I bet none of the academics doing any of that work let their kids have TVs in their rooms, or let their young kids watch a lot of TV.
One really interesting summary thing I read today - basic summary, paying on facebook / games (aka 'cognitively active screen time') may be better for your kids than watching tv. Lots of interesting stuff about screen time and under 5s also.
Also, quite a lot of evidence that increasing TV time may lead to higher likelihood of getting fat (or getting 'metabolic syndrome', essentially the same thing), independent of physical activity. Which probably suggests it's better not to have TV in their room where time is to some extent uncontrolled.
All this stuff is pretty easy to find, you just need to google scholar for it, much of it is publically available - http://scholar.google.co.uk/scholar?q=screen+time
It is often worth looking at the names of people when academic studies are reported, and at least googling and reading the abstract to see what the study actually said.