A part of the phenomenology of healthy full-blown love is that one sees that the beloved is such that one would have been remiss not to have recognized her lovability by loving her. The phenomology of healthy full-blown love is not misleading. But it is possible to have a healthy full-blown love for any person. So one should love everyone. For consider some person, say Sam. If one did have the healthy full-blown love for Sam, one would have correctly seen that one would be remiss in not loving Sam. But whether one would be remiss in not loving Sam doesn't depend on whether one in fact loves Sam. So, it is true that one would be remiss in not loving Sam.
In my previous post, I started the argument by noting that if you have full-blown love, you should continue loving, and yet I concluded that the conditional can be dropped—you should love (and continue loving) everyone. But why is it that the conditional had a special plausibility? I think it's because of the above phenomology of love. It's not that only the people you love are such that you should love them. But it's that by loving them that you best come to see that you should love them. Healthy love isn't blind: it sees our neighbor as she really is.