A very interesting observation. However, rather than people being ignorant of history, this dilution of the meaning of terms such as a racist, nazi or stalker might have more to do with changing associations with time.
We may have moved from the forms which originally symbolised these words, but since such extremities are rare in the world today, we tend to think of them lightly.
For example, the terror that was attached to the word 'Nazi' is seldom treated with the aura of despicability and dread as it was 50 years ago - during the times Nazism was actually prominent. Modern users of the term know the word and understand what it stood for but can't identify with the level of feeling our forefathers, who actually lived and witnessed the terror nazism unfolded, felt firsthand - therefore the meaning of the word no longer brings forth that accompanying feeling that our forefathers felt and perhaps which is why modern day people (probably the younger generation) tend to use that word too loosely. And that's what is happening with a lot of words.
To continue on a little, the issue is that the practices of many of these flawed philosophies are rising again at an increasing rate. Perhaps it is because of the dilution of the term through a lack of understanding of the reality of what they stood for. History repeats for reasons.
How I see it is that if words such as these are allowed to be diluted, when the reality of the past arrives again, people will not recognise it for what it is and think it is something new when in actual fact it is just a reiteration we no longer have a word for.