To be honest, you can only realize homophobic behavior for real if you are involved and affected.
Your discussion about the word "gay" and it's original meaning might apply to the English language but not to the German for example. Whereas "schwul" is also used as negative attribution like "gay" in English, it never had a different meaning but "homosexual male".
Clearly to me, using the word gay as insult or negative attribute is homophobic, because an equivalent happens on all languages, regardless if the word for gay had another meaning in the past or not. Being gay is still something people consider as weird - especially because it's not (always) obviously noticeable. So using the word gay as insult clearly refers to the assumption that the attributes object is not worth being considered as normal but as weird and therefore lame , like gays.
Personally I don't care if people call stuff "gay", but not calling it homophobic is wrong on so many levels.
Anyways I dislike the general attitude of the lgbt community to expose themselves as "suppressed minority". Yet I understand why they do it. Being lgbt isn't an obvious attribute, like being black or having blonde hair, so you quickly consider yourself as a lonely outstander since you never can see the homosexuality in someone without asking explicitly for it.
Also saying that "stuff like discrimination isn't that common in a modern society anymore" is quite naive because this isn't the case. You can be lucky if you never had problems, but I can not imagine that there is any lgbt that did not suffer from stuff like that. Lgbt people usually get entirely reduced to the fact that they are lgbt. In my case, many people are not seeing the person I am, but only the gay guy in many cases. Also many of my actions tend to be concluded by others to my homosexuality. It is bothering that everything you do will be reasoned with you being gay.
People define themselves or get defined quite often through a sole attribute.
I am really not that kind of person that would put himself into the corner of the victim, discrimination happens everywhere and will always happen. You can not avoid stereotypes, you simply have them.
The only thing that I wish for in future that homosexuality starts to be considered as normal and therefore not even worth mentioning or discussing. So it should be a normal attribute like body size, hair color and religion.
But every time I tell someone that I am gay, the first reaction is "Oh. Really? Well, I have nothing against gays but I couldn't do that." I can't remember that, when telling people that I have blonde hair, they reacted with "Oh. Well, I have nothing against blonde people." - they simply don't give a fuck.
Also it disgusts me how lesbians are widely accepted (e.g. watching these nasty late night porn ads on TV, where two girls are clearly do things with each other to turn on the males) But when two naked man rub their body on each other, it suddenly is a huge deal and people run away and vomit in every existing corner.
This is more discriminating for me than anything else right now.
Also it disturbs me that whenever a gay couple appears in a tv series, it's something special and worth exposing. Why? Shouldn't it be normal? What even discussing it then?
So much about my thoughts. I could tell you the story of my life, but that would also include to tell how I got my previous convictions. So not worth mentioning.