"Once I purposely killed a mosquito... I felt really guilty afterwards, though. "
when you'll go to a place with thousands of mosquitoes, at first try not to give too much attention to them because you think "well, they are just another creatures with their rights to live", and then after a very few minutes you will acknowledge that they will just drink all your blood till you die if you don't do anything, you won't feel guilty by killing them anymore :evil