the situation at the time was more dangerous and potentially explosive in nature if the police had got into a standoff with youths. it would have been a magnet for others across the city to come down to.
as people are leaning on the arrest issue, in a confrontational situation, too many people would have been leaning towards the rioters if things turned bad. ie ''pakistan khappey'' track. with no zardari infront of each person to say ''pakistan na khappey, na khappey, naa khappey'' a potential mini disaster has been averted (shuker Allah)
if the rioters came from the procession, they had already chosen ''pakistan khappey'' its more popular then acknowledged. perhaps mr mirza knew this aspect all too well, but in anycase i agree with his decision