We also express love for G-d by being keen to defend His name and His standing in others’ eyes. For in fact there are individuals who simply haven’t the sense of familiarity with G-d that you might have, and you are thus duty-bound to defend His “reputation” to them.
Now, some of them have either never sensed His presence in their lives or were never taught to catch sight of Him in the distance and to invite Him near, so their reticence is understandable albeit misbegotten. It’s easy enough to share your love of Him with such individuals, in that they only need to be introduced to G-d by your lights.
Others, though, are what can only be termed out-and-out “enemies” of G-d. They despise the very idea of a Creator and His interactions with the world, and try to have others do so too. Those who love G-d would go out of their way to dissuade these lost souls from their wrongful ways and would defend G-d’s standing to their faces.
In fact, our sages point out that anyone who “has it within his power to rebuke” someone like that but doesn’t is “no different than he” (see Shabbat 54b), because he didn’t go about actively defending G-d’s name.
And as Ramchal puts it, “the reason for this is obvious. One who loves his friend simply couldn’t stand seeing him attacked or abused, and would certainly come to his aid. So in that same spirit, one who truly loves G-d could never endure seeing His name being profaned, G-d forbid, or His commandments being overrun”. And they’d steadfastly defend Him.
The point of the matter is that G-d’s being belittled or dismissed would irk you if you truly loved Him. In fact, the degree your heart hurts when you see others besmirching G-d’s reputation marks the level of your piety; as truly pious people would surely be despondent when their Beloved was being defamed.