It shouldn't be hard to understand just because you're straight. Imagine if someone was Jewish and told you their grandfather was dead, would you just be like "oh did he die in Holocaust?" Or in a less extreme example, if you saw an overweight woman and said "oh are you pregnant?" as if those are defining characteristics of being Jewish or female.
The fact that you see a gay man who looks like he may be sick (but could've just been really old, I didn't realize he had cancer either) and automatically link that with him having AIDs is disturbing and disrespectful. Learn not to reduce groups like that.
Well there is a difference between saying something to someone's face and posting on a board. As for the holocaust question? Sure, if we had that kind of relationship, why not? And as for the pregnancy question, didn't stop you speculating Beyonce, Ciara, or Rihanna's pregnancy. Why is it no longer insensitive to you then?