Who says that the reason for loving a ger is because we were gerim in Egypt? That is only a reason to make us sensitive to how they feel (I would extend this to making deprecating comments about other ethnic and religious groups).
Who says? Hashem says so himself in two pesukim. One is vayikra 19:34, where the pasuk says “you shall love him as yourself, for you were gerim in the land of mitzrayim”. The other pasuk is devorim 10:19, “and you shall love the ger, for you were gerim in the land of mitzrayim”
We don’t need rabbi kook’s “ahavas chinam” philosophy to explain simple Hebrew translation of pesukim. I’m not even going to touch your conclusions about how we should not disparage false ideologies. Sheker sonayso ve’esahayva, ki torascha ahavti (tehilim 119, 163) falsehood i despise and am disgusted by it, because i love your Torah”. I’ll go with tehilim over a diyuk in a controversial rabbi.