Just one incident should not change the feelings from "an average Pakistani is similar to us" to "all Pakistanis are terrorist sympathizers/terrorists/suicide bombers". It's too drastic a change. A few Pakistanis might have been involved in the attack, but it does not mean that about 180 million Pakistanis had anything to do with it. I can assure you, no Pakistani rejoiced over these attacks, just as no Pakistani rejoiced over the Mumbai or Delhi HC bombings this year.
I think India is going through a phase of "ultra nationalism/patriotism", & whoever goes against this convention is labeled an India hater/anti-Indian. Pakistan is seen as a hindrance, a spoiler to India's progress, so "anti-Pakistanism" is high. While anti-Pakistan government/authorities feeling is justified for them, there is no reason for Indians to hate every Pakistan, & label them as a terrorist or suicide bomber. Most Pakistanis are able to distinguish the actions of a government, & the people. I don't think Indians have that capability, especially when it comes to Pakistan. Most Pakistanis hate the foreign policies of the US government, but have nothing against the American people. Americans that visit Pakistan are treated as honored guests, even in these difficult times of conflict (WOT). I have a feeling that ultra nationalism/patriotism makes Indians blind, making them paint all Pakistanis with the same brush they paint the Pakistan government/authorities with.