I'll paste you two passages about usage of "mankind" and "man" from my NOAD. It seems you were right, usage has changed for "politically correct" reasons:

USAGE of "man"
Traditionally, the word man has been used to refer not only to adult males but also to human beings in general, regardless of sex. There is a historical explanation for this: in Old English, the principal sense of man was ‘a human being,’ and the words wer and wif were used to refer specifically to ‘a male person’ and ‘a female person,’ respectively. Subsequently, man replaced wer as the normal term for ‘a male person,’ but at the same time the older sense ‘a human being’ remained in use.

In the second half of the 20th century, the generic use of man to refer to ‘human beings in general’ (reptiles were here long before man appeared on the earth) became problematic; the use is now often regarded as sexist or old-fashioned. In some contexts, terms such as the human race or humankind may be used instead of man or mankind. However, in other cases, particularly in compound forms, alternatives have not yet become established: there are no standard accepted alternatives for manpower or the verb man, for example.

Then:

USAGE of suffix -man
Traditionally, the form -man was combined with other words to create a term denoting an occupation or role, as in fireman, layman, chairman, and mailman. As the role of women in society has changed, with the result that women are now more likely to be in roles previously held exclusively by men, many of these terms ending in -man have been challenged as sexist and out of date. As a result, there has been a gradual shift away from -man compounds except where referring to a specific male person.

Gender-neutral terms such as firefighter and mail carrier are widely accepted alternatives. And new terms such as chairperson, layperson, and spokesperson, which only a few decades ago seemed odd or awkward, are common today.

I'll paste you two passages about usage of "mankind" and "man" from my NOAD. It seems you were right, usage has changed for "politically correct" reasons:

USAGE of "man"
Traditionally, the word man has been used to refer not only to adult males but also to human beings in general, regardless of sex. There is a historical explanation for this: in Old English, the principal sense of man was ‘a human being,’ and the words wer and wif were used to refer specifically to ‘a male person’ and ‘a female person,’ respectively. Subsequently, man replaced wer as the normal term for ‘a male person,’ but at the same time the older sense ‘a human being’ remained in use.

In the second half of the 20th century, the generic use of man to refer to ‘human beings in general’ (reptiles were here long before man appeared on the earth) became problematic; the use is now often regarded as sexist or old-fashioned. In some contexts, terms such as the human race or humankind may be used instead of man or mankind. However, in other cases, particularly in compound forms, alternatives have not yet become established: there are no standard accepted alternatives for manpower or the verb man, for example.

Then:

USAGE of suffix -man
Traditionally, the form -man was combined with other words to create a term denoting an occupation or role, as in fireman, layman, chairman, and mailman. As the role of women in society has changed, with the result that women are now more likely to be in roles previously held exclusively by men, many of these terms ending in -man have been challenged as sexist and out of date. As a result, there has been a gradual shift away from -man compounds except where referring to a specific male person.

Gender-neutral terms such as firefighter and mail carrier are widely accepted alternatives. And new terms such as chairperson, layperson, and spokesperson, which only a few decades ago seemed odd or awkward, are common today.