> Most of these people wouldn't have the ability
That's a dangerous assumption in any situation (it's never a good idea to assume your opponent is stupid). We do not have a monopoly on mathematics; you never know who has read [1]الكتاب المختصر في حساب الجبر والمقابلة.
> I wonder how the people who wrote crypto software and provide secure messaging services feel about terrorists and other bad people using their products
Are you going to ask shoemakers the same question? I'm sure most terrorist prefer the advantage of durable shoes when fighting. While I don't have any numbers, I suspect durable shoes have helped more terrorists than encryption.
...
The problem is you're anthropomorphizing technology. Each new technology is neither good nor evil (or neutral). I'll let Feynman explain:
I think a power to do something is of value. Whether the result is a good
thing or a bad thing depends on how it is used, but the power is a value.
Once in Hawaii I was taken to see a Buddhist temple. In the temple a
man said, “I am going to tell you something that you will never forget.”
And then he said, “To every man is given the key to the gates of heaven.
The same key opens the gates of hell.”
And so it is with science. In a way it is a key to the gates of heaven,
and the same key opens the gates of hell, and we do not have any
instructions as to which is which gate. Shall we throw away the key
and never have a way to enter the gates of heaven? Or shall we struggle
with the problem of which is the best way to use the key? That is,
of course, a very serious question, but I think that we cannot deny
the value of the key to the gates of heaven.”
Encryption is just a tool, and like every tool that has ever been made it will occasionally be used jby bad people doing bad things.
We keep learning more and more science and technology, and I don't think it is truly possible to stop that trend. I suggest we start finding ways to live with each other in the presence of technologies like encryption, because he problem is only going to get worse. We, as a species, are going to have a serious problem if we haven't learned that lesson by the time someone invents a way to make nuclear weapons with common household parts... or some unknown technology that is even worse.
[1] https://en.wikipedia.org/wiki/The_Compendious_Book_on_Calcul...