This is not how taxation works.
Goverment does not tax the money sent from abroad right away, rather there are certain charges being deducted by the bank/intermediary involved in the process whenever foreign currency is sent to Pakistan and the Government gets foreign reserves equivalent to the amount being sent (this is why Hawala is illegal because then the Goverment loses foreign exchange reserves).
The taxation works on a different principle depending on whether a person is a resident or a non-resident.
For a resident, both pakistani source income and foreign source income are subject to tax; and for a non-resident, only pakistani source income is subject to tax. This stage comes later at the time of filing of the income tax return, not at the time when money is being sent from abroad. Furthermore, if a person has already paid tax in the country of foreign source income, then he is not required to pay double tax in Pakistan after showing proof of documentation (with countries where double taxation agreements are signed by Pakistan).
Secondly, this is not money laundering, money laundering involves a covert scheme where black money (money earned through illegal means) is mixed with white money so that the black money also appears white and legal.