Is something not right in this?

Person A- Religion that is just sentimentatlity is utterly worthless.
Person B- But religion isn't just that! It is more than that!

Person A: Religion that is just sentimentatlity is utterly worthless.

This is just an opinion. One can agree or disagree, or perhaps ask for more clarification.

Person B: But religion isn't just that! It is more than that!

Seems like a reasonable response. Person A is specifically addressing one kind of religion (i.e., religion that is just sentimentatlity), which may or may not be the kind of religion that anyone actually practices. Person B's response implies agreement person A and continued to make a point. Technically, Person A could respond "I never said it wasn't." It is a strange initial comment by person A to which the point he or she is trying to make seems unclear.

Conversation continues....
Person A- Its time for religion to actually have a connection to real life.
Person B- It DOES have a connection to real life!
Person A- We need to take what is so familiar to us and have it connect with us somehow today!
Person B- By being appreciative and accepting of our past, not disdain for it!

So Person A is essentially claiming.

Some religions are purely sentimental.
Sentimentality is worthless.
Therefore, religions are worthless

Following Dr. Bo's criteria:

It must be an error in reasoning not a factual error. I can't find any error in reasoning in the first statement. As Dr. Bo responds, it is merely an opinion.

Sentimentality is worthless. (Argument from Ignorance)

This is a sweeping over generalization, if not an outright falsehood (deception?) or false premise. I don't think we need to argue the usefulness of the wide range of human sentimentality. If we restrict this statement to mean religious sentiment ONLY we might point out that Stephen Jay Gould describes such religious sentiment as Non Overlapping Magisteria (NOMA). Joseph Campbell refers to it as the Mysterium Tremendum. The great ethnologist Leo Frobenius describes creative epiphany as an "eruption of emotion". William James regards them highly and includes such outlier revelations in his Varieties of Religious Experience. Certainly there is a solid argument that religious sentiment may be complex and subjective, but hardly worthless.

Therefore, religions are worthless.

Now, here, I think we have an ambiguity that assumes something true of the part is true of the whole or a Fallacy of Composition. (Of course, this applies more to my interpreted syllogism than the original question.)

BTW: I am reminded of a lecture on the Bhagavad-Gita by A.C. Bhaktivedanta where he similarly declared:

“Religion without Philosophy is sentiment, or sometimes fanaticism, while Philosophy without Religion is mental speculation.”

Person A: But If there is no staying power in that Past, if what we see in It doesn't somehow affect how live: useless right?

Person B: If my doctor told me how to get better but I didn't let this inform me; it would be worthless because I decide not to let it, by my own choice. This doesn't Prove in itself that his advice is worthless. Objectively, it may have a positive affect but I'm not letting it have any.

Hey Joel,

Of course, we can evaluate the neuroscience behind the Evolution of Misbelief (See Dennett and McKay) which maintains that religions and beliefs
were (useful) 'cognitive mechanisms adapted for other purposes' i.e. pareidolia, Hyper active agency detection, mythology, storytelling, etc)

So, as far as evolutionary psychology goes understanding the beliefs, rituals, crafts and artifacts of the Past are extremely useful to a myriad of scientific disciplines, e.g. Archaeology, anthropology, ethnology, architecture, history, mythology, etc.

However, to determine the logical fallacy as you state it I'd break it down to something like this:

For the Past to be useful it must have staying power and affect our lives today.
Therefore, if past beliefs have no staying power or affect our lives, they are useless.

Off the bat I have no problem with the claims other than the conclusion of uselessness. I could interpret that as either a hasty generalization or the Pseudo-logical fallacy often referred to as chronological snobbery.

Chronological snobbery is an argument that the thinking, art, or science of an earlier time is inherently inferior to that of the present, simply by virtue of its temporal priority or the belief that since civilization has advanced in certain areas, people of earlier time periods were less intelligent.