Editor's note: LZ Granderson is a CNN contributor, a senior writer for ESPN and a lecturer at Northwestern University. He is a former Hechinger Institute fellow and his commentary has been recognized by the Online News Association, the National Association of Black Journalists, and the National Lesbian and Gay Journalists Association. Follow him on Twitter @locs_n_laughs. The opinions expressed in this commentary are solely those of the author.  (CNN) -- I still remember the chill that came over me the day my middle school history teacher showed the class a documentary about the Holocaust.  Millions of Jews were systematically isolated, corralled and eventually murdered by the Nazi regime. It's a horrible blemish on the history of mankind, one that is rarely brought up lightly. It's one that is recognized in museums, dramatized in film and taught in middle schools like the one I went to nearly 30 years ago.  And yet, despite my continuous exposure to the retelling of the Holocaust, it wasn't until I was in my mid-20s that I learned Hitler had also isolated, corralled and murdered gay men and lesbians during this time as well.  Right now I can hear the voices ask: What does it matter?  I had graduated from high school before I learned some of the greatest voices during the Harlem Renaissance and civil rights movement -- Lorraine Hansberry, James Baldwin, Bayard Rustin -- were members of the LGBT community.  It was in graduate school when I first heard the name Harvey Milk. I was a working journalist before I was told about Dave Kopay, the former NFL running back who came out in his 1977 autobiography, "The Dave Kopay Story."  And now the chorus of voices ask: So what?  Over the years, I am proud to say I have amassed a decent personal library. Most of the books are about history: presidential biographies, wars, social justice movements.  And yet, it was only this week -- thanks to longtime civil rights activist David Mixner -- that I learned Congress once debated passing a law forcing gay men to wear tattoos and corralling those who were HIV positive into internment camps. Yes, just like the Jews. Just like the gay men who were next to those Jews in Nazi Germany but have since disappeared from our history books.  It is here where the cynic wonders: Who needs to know?  With the overturning of "don't ask, don't tell," the sweeping changes in marriage equality, the presence of open LGBT people working in the White House, on TV, even in professional sports, there may be some who believe the heart of homophobia no longer beats. Much in the same way others believed the burning of bras slayed sexism and the election of President Barack Obama was racism's death knell.  One of the most powerful CEOs on the planet has announced he is a proud gay man, and while I may be hesitant to characterized Apple's Tim Cook proclamation "brave," it is nonetheless important.  Just as Hansberry and Rustin and Milk were there -- working for the greater good, changing the course of global history, woven into the fabric of humanity.  The voices may ask: What difference does it make? Let the absence of LGBT people in our retelling of our history be the reply.  For if being gay, lesbian, bisexual and transgender truly did not matter, why then must we fight to have our contributions recognized?  Why then, when California became the first state to require our stories be included in the history books, was it met with resistance in 2011? That conservative state Assemblyman Tim Donnelly described the day the bill was signed into law "sad" as if simply learning that a group of people existed infringed upon his Constitutional rights.  To be honest, Cook's announcement is no great shock to anyone who has been paying attention to the rumor mill. But by owning his truth in such a public fashion, Cook is not only rebuking the tendency many LGBT baby boomers still have to hide, but he is also refusing to allow his silence to render him hidden.  When the middle school history teachers speak of him, they will have his full story to share.  Going forward, chants of "who cares?" will accompany nearly every person of note who chooses to come out publicly. Even among LGBT people, shoulder shrugs will not be that uncommon, as if debates about internment camps happened in the 1880s and not the 1980s.  Yes, the country is different, and being gay is no longer shocking.  But it is a mistake to confuse that progress with Cook's announcement having no importance. For far too long, the story of the LGBT community has been scrubbed from our education, contributions erased and existence relegated to the poorly lit corner of bookstores under the banner "Alternative Lifestyle."  We are not a "lifestyle." We are a people, and we were there.  Read CNNOpinion's new Flipboard magazine.  Follow us on Twitter @CNNOpinion.
LZ Granderson: What does it matter if someone such as Apple's Tim Cook comes out as gay in today's world? History tells us it matters a lot.