I want to add something to the answer of @AlexanderSKing:
The question may be reformulated as "Should I be dogmatic?".
Dogmatism can be understood as stating a "truth" and not only defending it (by rational argument), but also discrediting every other weltanschauung.
In not respecting a religion, you implicitly are dogmatic: You say that the foundations of this religion are untrue and the foundations of your weltanschauung are true. Dawkins is a good example for a dogmatic position. But the point Popper is making is that as long as the opponent is not dogmatic, you can tolerate him and his weltanschauung, taking him back into rational discourse.
But in not tolerating religion, are you better than catholic church in crusades and inquisition or islamic terrorists of Boko Haram or IS regarding dogmatism and its related mindset?
This question is not as rhetoric as it seems, though of course not accurate. But for the sake of the argument go on reading ;). You will, I assume, never establish your view by force. But you cannot respect the person by disrespecting her religion either. Because the weltanschauung is an integral part of the person, it is a part of the autonomy of this person. And dogmatism is in fact rejecting a part of a person's autonomy, and by this her dignity. They do reject the dignity in total, but assuming that dignity is absolute, the connection, although harsh, is there.
The borderline of your freedom is the freedom of others. Popper is reformulating the old idea of a social contract: (Hobbes), Locke, Rousseau, Kant, Fichte, Hegel, Rawls. As long as the weltanschauung of others does not harm you in practical execution, you have to tolerate it, no matter how your feelings about it might be. That is why social contract theories are often theories of natural law, restricting practices, not opinions. That's the reason why the above mentioned cannot possibly be tolerated even in the widest sense. But dogmatism should not be tolerated in any way.
I also can't understand people that believe in religion. Sometimes their deep belief and the actions based on it even make me angry. But in order not to be dogmatic, I have to tolerate their belief as long as it does not have direct consequences for my practices (or, in a wider sense, autonomy). I have to respect their autonomy and dignity.
Edit regarding the dogmatism/respect dichotomy
In some sense, tolerance is a direct outcome of respect. Respect in the kantian (and most philosophical) meaning(s) is not to be confused with the feeling of sympathy. You do not have to like a person in order to respect her. For Kant, respect is due to the dignity every moral agent (i.e. person) has. And you do not have to think that there is a God to act respectful towards religious persons and their religious sentiments. See more modern approaches like Rawls or Axel Honneth's Theory of Acknowledgement which are also working with respect.
It is not disrespectful to say that you think that their belief is wrong, it is disrespectful to say that your truth is objective and they are talking nonsense.
You should rather ask for the meaning of what they say. And if they are not dogmatic, it will be that they believe in the existence and that there are proofs for the existence of God. This will be the point you will be able to enter a rational discourse with one another.
Dogmatism in a more traditional understanding is saying that a particular religion is not only about statements to believe in, but about actual objective facts.
This whole argumentation is from a kantian view with kantian concepts and terms, the terms are well stated in his Metaphysics of Morals, part 1, Ak. 221-28 or in this argumentation. They are technical, philosophical terms. Do not confuse them with common language usage. And this argumentation is deliberately overdoing it to point out the problems and differences of both the positions of the opener as well as the kantian answer.