All Atheists are Immoral

A statement of the type "all atheists are immoral" is

1. A fallacious statement because one is making an inference from a group which is not relevant to the question at hand - "who is moral" - since one cannot tell just by whether someone believes in god(s) or not as to whether they are moral or not. The "all" in the premise makes it a hasty generalisation and the conclusion does not follow, it is a non sequitur.
2. A statement of prejudice because one is not following the principle of "innocent till proven guilty" and instead prejudging the guilt of such a group on these fallacious grounds.
3. A statement of bigotry because one is assigning this guilt to any perceived members of this group.

Now (assuming you have no other prior information) when someone makes such a statement one does not know whether they either guilty of:

1. Moral negligence: Being ignorant of the moral implications of such a statement is not a defence. Now if they have failed to consider or examine this, what any reasonable person is capable of doing, their failure to ensure that this judgemental claim is on firm foundations and not in error is to be guilty of intellectual negligence. Considering they are possibly tacitly claiming the moral high ground and, certainly, given the moral implications of this statement, this makes it moral negligence. In the light of being challenged they could revise their view in which case they would not make it in the the future, if they do then they are certainly guilty of:
   
2. Bearing false witness: They know full well this claim is false and make it anyway. They are therefore clearly guilty of prejudice and bigotry.
   
3. Being a moral cripple: They need to believe this to be moral themselves and losing this belief would make them immoral. If so, they are a cripple needing the crutch of the church to be moral. Then their specific church is morally culpable for manipulating them into this reliance - turning them into a cripple - and putting them in the ironical position of promoting such immoral views as "all atheists are immoral".
   
4. Something else.

When this statement is brought up do not offer your own morality in reply, if you do you are tacitly acknowledging their tacit claim of the moral high ground. Instead, I recommend that this is what needs to be challenged and to become the topic of conversation - after all it is they that brought it up - and, at the same time, to not fall into any of the traps that the statement utterer has possibly made themselves. Still we do not know until we ask them what their guilt is and if so of what type. This means to use the principle of "innocent till proven guilty" - to not reply to a statement of prejudice with prejudice - that is prejudgement of the guilt of the statement utterer - either. (Ahem.. although on the principle of ethical reciprocity, they have no defence if you were to, unless they reject the golden rule... )

Of course, when it comes to professional representative of an organisation, then this is already sufficient evidence they they are most likely bearing false witness and promoting bigotry and prejudice and so deserve condemnation and sanction and the same goes for anyone who supports or defends them.

(Note: I have covered this topic before but this is a more succinct and up to date view.)