Indeed, a very interesting topic..............
I think the concept of 'unconditional' love is tightly tied to one's definition of the word 'love'.
Because for most people I think the word includes both and adjective and verb tense.
If we define 'love' as our deep desire for someone's (everyone) health, happiness, good life etc, it's easier to generate a feeling & concept of universal, unconditional love.
However, when we must move from philosophy to action and actually play a role in bringing positive things to others, it can get to be hard. There are certain behaviors, attitudes, beliefs etc that make us unable to support someone in their quest for their happiness etc. Because their happiness may include unhappiness or harm to others.
So does this mean that the concept of 'unconditional' love cannot exist ?
Depends on your definition of love.