[smsm42]

They don't have phasers that can be set on stun either.

There are chemicals, of course, that can cause loss of consciousness, but any that causes loss long enough to be effective against the force of 400 people hiding in urban setting, would kill most of the civilians. It's not random that when the human is anesthetized it is done in controlled setting by an experienced doctor with very precise mixture of chemicals - it is very dangerous to do it and exceeding dosage could be lethal or cause permanent harm. Military weapon can not adhere to such dose requirements so it will be either ineffective or extremely dangerous.

Read this: https://en.wikipedia.org/wiki/Moscow_theater_hostage_crisis

This was the easiest setting - everybody in one enclosed building and civilians can be treated within minutes after the attack is done. Imagine doing this in a complex urban setting, with multiple buildings, with 10 times as much enemies, where both enemy and civilians can be anywhere. It's just impossible to do without killing everybody and leaving the place a chemical wasteland.

And, of course, on top of that, if US military does it once, Talibans get gas masks. But civilians would not, so the only effect would be killing civilians.