The US and UK governments simply don't want people using Kasperky's products because Kaspersky will not white-list their Malware. It slows down the US and UK governments mass spying operations. Kaspersky is the best there is and, although Kaspersky's signatures are top notch their zero day protection is equally as good, so good in-fact that the US government used it themselves out of all the other vendors they could have chosen, some of which are US security companies.
Kaspersky have detected a fair amount of US government malware/spyware and that's going to ruffle some feathers. It could be a case of the US government asking Kaspersky Lab to whitelist all their tools and Kaspersky Lab refusing to do so. So, the US hot back by trying to ruin Kaspersky's reputation, after all if the US government can get millions of users to drop Kaspersky then Kaspersky white-listing their tools isn't so important anymore.
This is all just speculation on part of course. There could be much more to it or much less. I doubt we'll ever know the real reason for the ban.
I do find it strange that Checkpoint, an Israeli based security company use an older version of Kaspersky's engine and! Kaspersky's sigs in their Zone Alarm products. Do they use the engine because it's top notch or to reverse engineer it or for some other reason.
Their could be real evidence against Kaspersky but said information could be very sensitive and reveal the methods about how it was obtained that the US simple cannot reveal.
Personally, on My Windows Machine I use Kaspersky's products, I like them, I trust them and, as a suite KIS is amazing especially when you really tweak it. And, until I see any evidence that the allegations against Kaspersky are without a shadow of a doubt true I'll continue to both use and recommend Kaspersky's product's
Lets hope we find out more soon.