* "Spiritual" harms or uncertain consequences in an after-life or in the future are much too subjective and speculative to be portrayed on the scale above. It is impossible to objectively gauge or agree on such things.
Does being one of Jehovah's Witnesses result in harm? The objective answer is:
Membership is "Mostly Harmless"
The truth of this is borne out every day by the lives of the more than 6 million Jehovah's Witnesses who are functioning as normally as anyone else in the world without any significant harm resulting from membership. With some rare exceptions, Jehovah's Witnesses are healthy and productive members of society who are living their lives normally. Being one of Jehovah's Witnesses may be reductive, it may be restrictive and it may be limiting, but it is not harmful. It is for this reason that scientists like Singer and most sociologists do not categorize Jehovah's Witnesses as a cult despite their being some cultic qualities among the group.
The fact is also borne out by the clear evidence that thousands of Jehovah's Witnesses and non-baptized associates leave the religion each year without displaying any physical, emotional or mental harm whatsoever, even though they may have been among Jehovah's Witnesses for many years. This is not the case with cults in which it is rare that the ex-members don't show some trace of harm from their time spent within the cult, at least for a time.
Having said the above, there are several areas of concern with the culture of Jehovah's Witnesses. Some of these are admittedly potentially harmful and require discussing and are the reason why I give a qualified "Mostly Harmless" answer.