It's not bestowed by the First Amendment. If that was the case then it could be taken away simply by a constitutional amendment. The government doesn't grant you that right - get that idea out of your head immediately. It's dangerous.
I think our rights as it says are endowed by our creator, whether you believe in god or not, for the very purpose that the government cannot take them away.
Both of you are attempting to argue philosophy with a reality based person. I understand your thoughts, but the factual reality is that your rights in this country exist solely because the constitution grants them. The courts , the .gov, the .mil, law enforcement, and activism preserve them.
They (your rights) can in fact be taken away simply by amending the constitution. There are four routes an amendment to the constitution may be made
Proposal by convention of states, ratification by state conventions (never used)
Proposal by convention of states, ratification by state legislatures (never used)
Proposal by Congress, ratification by state conventions (used once)
Proposal by Congress, ratification by state legislatures (used all other times) Source
There is no language in the constitution forbidding modification of or repeal of any amendment. If there is, please source it.
Oh, and ideas in and of themselves are not dangerous. Acting on them (ideas) may or may not be (dangerous that is).