It is absolutely nothing to do with him or the family, although some have used that as an excuse (which in my opinion is far worse that 'outing' someone) No one can know how he would have behaved or what he would have wanted because the world today is so different from the one he knew.
The Rainbow badge is a symbol for the gay community
"A symbol of diversity
Finally, the rainbow is a symbol of diversity. Although myths and stereotypes portray all gays and lesbians as having a single, monolithic “agenda”, the reality is that ours is an extraordinarily diverse community. Across all races and cultural backgrounds, across all languages, with or without disabilities, across all religions, our communities continue to flourish.
Sometimes, our own communities are divided between gay and lesbian, between “gay” and “queer”, between those in big cities and those in the suburbs and small towns, between “assimilationists” and those who want to live apart from the mainstream. While diversity poses its challenges, it is also enriching. There are as many opinions as there are people. There is no lesbian, gay, bisexual or transgender “lifestyle”, there are only lesbian, gay, bisexual and transgender people. Millions of us, each one unique. This is our strength.
So, why should we bother?
• Because people are still denied jobs, promotions or denied accommodation because of their sexual orientation.
• Because gay teenagers are disproportionately at risk of suicide.
• Because people are still beaten or murdered for being lesbian, gay, bisexual or transgender.
• Because we are still made to feel uncomfortable when holding the hand of a partner while walking down the street.
• Because our materials are still censored by the government and banned from schools.
• Because our relationships remain unrecognized in hundreds of federal, state, provincial and territorial laws.
BY CELEBRATING OUR PRIDE TOGETHER, WE REMEMBER OUR PAST, AFFIRM OUR FUTURE AND PROVIDE IMPORTANT VISIBILITY WHICH ADVANCES OUR STRUGGLE FOR EQUALITY "
So those who refuse to wear it are undermining these ideals.