Keeping details about yourself secret online is always a smart option regardless of what they are. I sure as hell ain't going to tell everybody online I voted for these people, and these are my bank details, this is where I work .... so on and so forth.
Sexuality is one of those 'taboo' things that rampages around the internet like an enraged bull however and personally I find it depressing.
I don't care if somebody is LGBT ... I couldn't give a rat's arse if a friend is gay/bisexual trans/etc. Why? Because they were gay before I was friends with them, they'll be gay after I drift away o/s and stop being a friend to them (yes, I'm one of those people that can't maintain long distance relationships of any sort), and frankly I'm not interested in them beyond being friends (that and crossdressing on occasion is fun when you have gay friends and want to hang out with them one saturday night >:]).
That being said ... if a close friend said they were gay, and I had known them for years and they have known they were gay for years, I probably wouldn't be so close to them. But that's purely because I'd be kinda hurt that I considered them to be a close friend, but they didn't trust me enough to open up until just now ... because I pride myself on my mantra of keeping things told in confidence of secrecy secret regardless of who it is .... (even if I had a severe dislike of the person in which confidential material concerning the individual was availed to me by word of mouth).
That being said ... it depends on what type of 'online' we're talking about.
The internet isn't all the same thing. From a technological standpoint it is, but to the various audiences that go into it, it is not.
For example ... online shooters ... WHY THE HELL WOULD SEXUALITY BE AN ISSUE IN A SHOOTER? Sure you get insults thrown about someone's sexuality, but people having a tantrum about it on mic when the game's chat system should be exclusively refrained too "That's what happens when you noobtube ... sow the wind asshole" and "they're camping at X", or the like.
Personally it bugs the hell out of me ...when I'm gaming, I want to talk shit ... and in return I get it thrown back at me 2 minutes later. But one game ... it was unbearable. 'So what if i'm gay?' I think was a response to someone's comments .... which, suffice to say to anybody whose played any online shooter with voicechat enabled, concluded with a torrent of 13 year old and redneck assholes talking in a manner which I will only dub as 'XBL dialect'.
My comments aren't nice ... but it's more 'sledging' than insults ... reserved to noobtubers and campers when you clocked them, and personallyt I will never use homosexual rhetoric (like the F-word we are acquainted with so completely online) ... especially since '*****' and 'noob' are somewhat slightly more based in reality. But the homophobic reaction...
So, to end my rant prematurely, yes ... there are idiots out there .... yes most of them are probably 13 year olds or rednecks ... no they will never EVER change ... and yes, depoending on what forum (such as online games) LGBT internet goers perhaps shouldn't say anything for the sake of everybody's enjoyment.
That may sound harsh, but trust me ... you're playing a game to enjoy yourself ... and you should be secure in the knowledge that 90% of the people that will be talking crap will probably get their mouths washed with soap the day their mommy catches them trashtalking.