It is worth noting that there is a distinction between coasting in gear but with the clutch depressed and coasting in neutral from a legal standpoint, and thus is really hard to enforce on a stickshift.
Most of the regulations I've seen refer specifically to coasting in neutral.
Officer: You were coasting in neutral.
You: I was in gear.
repeat ad nauseum.
To demonstrate this distinction, have a look at washington commercial vehicle law:
RCW 46.61.630: Coasting prohibited.
" RCW 46.61.630
Coasting prohibited.
(1) The driver of any motor vehicle when traveling upon a down grade shall not coast with the gears of such vehicle in neutral.
(2) The driver of a commercial motor vehicle when traveling upon a down grade shall not coast with the clutch disengaged.
[1965 ex.s. c 155 § 74.]"
Presumably a lot of the fear surrounding this law was before reliable synchromeshed transmissions and other safety equipment.