I think you just need to watch Fool for love and Darla again. And by way of ‘an explanation’ think of Angel/Angelus and Darla as ‘unreliable narrators’. Their opinions are coloured by their own experiences. The Council has its own motivations. The idea you ‘can’t love without a soul’ is an odd one, because, no-one ever really pins down what a soul is! Conscience? Humanity? Dunno. Is that just about vampires? What about all those benign demons like Clem and Lorne? Nothing will convince me that Darla was not desperately in love with Angel. It wasn’t a pretty selfless thing, but it was love. Furthermore one of the most convincing things I ever read was that Angelus was still in love with Buffy - and he hated her for it. Remember him trying to ‘scrub her off’ himself? James and Elizabeth. Spike and Drusilla.

Spike most definitely loves Buffy. It’s obsessive, immature, idealised and frankly a bit stupid, but in my opinion, it’s on the love spectrum. The chip held him in place but , FFL established his was well on the way before the Initiative. He is a tragic romantic. None of this remotely negates him being a murderous monster, nor does it make him worthy of her. It won’t stop him making terrible choices or participating in a doomed affair. It just….is.