Pretty sure that's not true?
If you mean 'open up' in that he and many other people working towards acceptance of the wider LGBTIQ community in the western world, then yeah..but this is only in the west. And as you should know, even if something is illegal, if people want something they'll look for it - case and point, every person on this site.
What DB did was amazing and wonderful. That's an achievement in and of itself. Few people will ever change the world they live in like that. Celebrate his memory and his achievements of his influence for what they are. Incredible in their own right.
I'm not in the habit of saying things (in seriousness) which I do not believe to be true, and I wasn't being ironic or sarcastic.
David Bowie was a huge icon for the breakdown of gender barriers because of his enormous influence on pop culture, which has had a global impact. He could've stayed in the closet, but he didn't.
As for "only in the west", that's mainly because other societies are in reaction. It is a reaction, though, which means the awareness of sexual liberty already exists as a paradigm. It's only a matter of time before it is realized, though I'm not expecting it to happen tomorrow.
If you don't think that western rock stars influenced Japanese pop culture enough to open up yaoi, I suggest you read the Eroica series.
Wasn't it normal for homosexual men in Britain to be arrested as sexual deviants and chemically castrated when Bowie was younger? It was risky to come out, even if he wasn't the only one doing it.
R.I.P. David Bowie. Thank you for your work in breaking down gender barriers, which helped open up yaoi!