So either you're correct and we don't care or you're not correct and we don't care. Speculation beyond that point is useless.
Oh no, we care, very much so. Any direct involvement of India in actively nurturing/supporting/training/deploying Islamist terrorism has drastic implications for us; not only at the regional level where we're currently engaged militarily, but also in the fundamentals of our bilateral relationship with India. People at the State Department aren't as stupid as we think they are, alongside the pentagon they do learn a thing or two from their past experiences. They are also well aware that the desire/intention/ability to raise disciplined and/or focal terrorism groups in this region is categorically untenable; which is why this conspiracy theory of us being "OK" with India using terrorism as long as it is aimed strictly toward Pakistan is absurd. The CIA and other intelligence agencies have a significant presence in Afghanistan and it would be naive to assume that they aren't keeping tabs on the Indian set up there, especially considering that their involvement in the post Taliban period was a joint venture with Iran. The point however is that given the long standing tensions between India and Pakistan and the latter's policy of using terrorism as a front line tool pretty much necessitates an intelligence network which India either has, or is trying to establish through various areas of Pakistan. This however does not mean that India is resorting to sponsoring and deploying terrorism at will as Pakistan does/did; and if that were the case, trust me, we'd take very serious issue with it.
This entire region (in it's current form) has since it's very formation six decades ago been marred in covert conflict with occasional bursts of overt warfare. Industrial quantities of insurgents along tribal, ethnic, religious and political lines have become endemic to the area and needless to say it is critical for each government to know about if not establish some level of contact with as many of these entities as possible. The difference however is that not all parties have similar relationships with terrorists groups and the nature of relationships themselves in their various contexts vary drastically.
Pakistanis desperately want to see India as an equal when it comes to sponsorship of terrorism (and everything else). Doing so would allay many misplaced populist notions/fears, assuage feelings of angst and humiliation brought about by the current state of Pakistan's affairs and it's perception in the world as a hotbed of Islamic terrorism; and defer confronting the greatest fear of all, that Pakistan has 'fallen behind'. The Mumbai attacks have also played a big role in promoting these feelings because for the first time in the history of this conflict a 'guilty party' and a 'victim' has been declared thereby relegating Pakistan to the defacto 'bad guy' status and elevating India to be the 'good guy'. The only way to equalize this disparity is by showing that India conducts similar kinds of operations in Pakistan. The public reaction to the Sri Lanka Cricket team attacks are pretty much self explanatory.
It is certainly understandable why people feel this way (and let's be honest, our posts fuels these insecurities even further among many of the posters here); but unfortunately populism doesn't necessarily translate into reality. India and Pakistan are NOT equals when it comes to sponsorship of terrorism. In fact, the relationship Pakistan has with Islamic/Islamist terrorism is very unique, and one would be hard pressed to find a single other state which plays a similar role and/or is suffering the similar lethal side effects of endorsing terrorism as a front line policy. No amount of dissembling, deflecting, denial and indulgence in mental gymnastics is going to change this. As I always say... the biggest disaster for Pakistan (and subsequently everyone else) will be to keep erroneously referring to and treating this problem as an infection when it is in fact an autoimmune disease.
