Using words in ways they shouldn't be used.

So I've been having a few debates on words that are used incorrectly. Three examples that I'll state are agnostic, atheist, and gay. All these words are used in the incorrect way based on what people who call themselves these things mean and/or what they originally mean. I shall go through the three and explain how many people use it and what people who call themselves that really mean.

Atheist- lack of belief in a god or gods

This word isn't a statement about what degree you believe. It just means that you have no belief in a god or gods. To determine how sure you are we need a modifier which is what agnostic is used for. It means you do not know if there is a god or not. This has nothing to do with what you believe about a god or gods existence just that you believe you can not know either way. This is called an epistemological standpoint - it has to do with what one knows. So by calling one's self just agnostic does not tell me or anyone else what you believe of god's existence just that you think you can not know for sure either way. So an agnostic can both believe in a god and lack a belief. Many times when given this people who call themselves just agnostic will come back and say that they don't not believe in god. To which i would say, "So you believe there is a god?" because if you do not not believe in god you believe in god because of the double negation that happens. Another common argument is that as an agnostic they would say, "I just don't know if there is one or not". Fine, I agree with that - but what do you believe about god's existence? Do you think he does or does not? To say you just can't know means you can be either one, so I would have to assume by default you lack a belief in god and therefore are an atheist (see above definition).

Gay- happy or homosexual

This word is sometimes used when saying something is stupid. I believe that by using it this way, it reinforces homophobes' beliefs on homosexuals. So therefore I think it should not be used in this way.

When explaining the above, I've come accross arguments such as "but I know people who are gay who don't take offense or don't think it's wrong to use it that way". First, I'd like to say that I would agree that people do not have a right to not be offended, but with this I would also like to say that by saying it as I have stated above, you are reinforcing someones else's hatred for these people and I highly doubt you would want that to happen.

Sigh, why don't people understand these comments? Can someone explain it to me?