> Secular folk disagree that religion is an optimal, or even necessary, way to do that good.
This is tricky.
As an atheist, sometimes quite a militant one, I think that religion is not necessary in principle. But, oh boy, there is a very long road from "not necessary in principle" to "we have a fully functional replacement, without bad side effects". And if you think you can simply throw away something that has evolved for millennia, replace it with a product of armchair reasoning, and get anything other than a complete disaster... well, seems like evidence is on the opposing side.
Fully replacing religion is a task that needs to be taken seriously. Otherwise you are not a real atheist, but a mere believer in a No-God Fairy that will somehow make things magically right after religion is removed.
To appreciate the complexity of the problem, just think about all the existing social classes: religion applies to most of them. Does your solution? Or are you proposing a morality which will e.g. work pretty okay for middle-class educated people with IQ over 130, but will result in a social disaster when average or below-average people will try to copy it? (Because, trust me, they will. People love to copy the manners of those above them on the social ladder; especially the bad ones.)
> You can walk the straight and narrow path without the carrot of eternal salvation or the stick of eternal damnation.
Oh, you definitely can, but will you? And what about the others? How much of current non-religious morality is built on inertia from previous religion? How long will the inertia stay after the original religion is gone. In general, do atheists in traditionally Christian countries invent the same morality as atheists in traditionally Muslim countries? (Heck, do even atheists from the same culture agree with each other?)
And if there is the "secular Way", who will be the one to teach it to the next generations? Who will pay the expenses of the teaching, solve the logistics, etc. With religion, we do have an answer: it is in the selfish interest of the religion (its institutions of power) to replicate its values. What is the answer for atheism? How many atheists will sacrifice their careers to make sure the next generation remains culturally compatible? Why would they? Will the whole atheist society just fall apart after a generation or two, when their kids decide that superstitions or cults are more cool.
Don't get me wrong...
I believe that this problem can be solved.
But also...
I believe that this problem is difficult.