Is this really a dangling modifier?

In a paper I recently wrote about Dr. Martin Luther King, jr., I used the sentence:

As a black man in the '40s, it was almost unheard of to go to college.

Someone suggested to me that this sentence contained a dangling modifier or an error of that nature. My sentence does seem to be quite similar to an example of a dangling modifier from Purdue:

Without knowing his name, it was difficult to introduce him.

Who didn't know his name? This sentence says that "it" didn't know his name. To revise, decide who was trying to introduce him. The revision might look something like this:

Because Maria did not know his name, it was difficult to introduce him."

Yet, I'm not quite convinced that this sentence is incorrect. Please clarify whether or not this is truly an error, and if it is, please offer some possible alternatives.

The example from your paper is incorrect, because you started out by mentioning a definite person "AS a black man", then followed up with "it".

This could be parsed as

• It was almost unheard of to go to college as a black man in the 40's.

But this might lead the reader to wonder "but how could MLK Jr. have gone 'as' anything other than a black man? In disguise, perhaps?"

A better way to say it, using AS, would be

• As a black man...King had very limited opportunities to go to college.

But your original would have been correct, if only you had used FOR rather than AS:

• For a black man in the '40s, it was almost unheard of to go to college."

Which could easily be parsed or rephrased thus :

• It was almost unheard of for a black man to go to college in the '40s.

The other example you cited is different. "without knowing his name" does not allude to a particluar person as SUBJECT of the sentence. So I would agree that it really is not incorrect per se. The implied clueless introducer is "one". If this sentence occurred in, say, a novel, we would know from context who that "one" was.

And more to the point, I believe the explanation of why that example was "wrong" is erroneous. In that sentence, "it" does not refer to an unnamed person—"it" is a placeholder referring to the situation "difficult to introduce him" (there's a name for such a use of "it", but I'm not a linguist).

Now you might say that the same is true of your sentence on your paper. All I can say is, you should have used "for", as shown above.