Hmmm...I don't know what A4A is?
My first thought is that you're expecting a great deal from a "blind date/hookup," eh? I can't say I've not been there and done that, allbeit rarely, and have to admit I've done exactly what you found to be offensive, but given the medium(s) you are utilizing do you really expect more? The more superficial the medium, the more superficial the resultant interaction is likely to be. If your only engagement with a person, pre-meeting, is via a few words and a select picture or two, I don't think it should surprise you that rejection is a very likely possibility.
These things said, my advice is to be as open with your sexuality as you are comfortable being--offline
. Now, don't misread that! I'm essentially highlighting your orientation, not your libido (although, yes, they are connected). I don't know you or your situation, but I find that the more open I am about who
I am in my everyday life, to include my sexual orientation, the more opportunity I have to meet and interact with others that are also open. More often than not, such interaction will draw a person away from the predominantly impersonal and seemingly emotionless online 'meeting' realm and into a more active arena in which others will be mutually interested based on more substantive measures.
This is not to say that online environments offer nothing or are intrinsically bad...far from it. You simply have to make mindful choices and judge your outcomes accordingly.