I think Fade90 got everything spot on. There is so much more than Angelus wrong with CAngel - and the possibility of Angelus was only one of many reasons Angel left Buffy. Cordelia, like Buffy, is still mortal - and Angel is not, meaning there is no chance of them 'growing old together'. Only one of them will grow old. It's going to get to a point where the relationship is ... awkward at best. Cordelia will want to go on holiday or have a picnic in the park, go to restaurants, do normal coupley stuff, and she can't with a vampire boyfriend. He will be stopping her from having a proper life and will be being selfish in doing so. Add in the danger of Angelus and how Cordelia, of all people, is always most worried about him returning plus the fact that Angel is pretty cheap and Cordelia likes to spend ... and this relationship is going nowhere.
I also think there's more to the Angelus aspect than 'uh oh we might unleash Angelus'. Yes, they can be careful, yes they can understand that it isn't actually sex with Buffy that triggered it - it was perfect happiness which could, in theory, happen any time anywhere but won't simply because Angel will never allow it to happen... but keeping that in mind - for Cordelia specifically - would require being quite clinical and scientific and detached about the whole thing (none of which are great romance words). In reality, it would eat away at her - how could it not? Every time they slept together and he didn't lose his soul it would be a little reminder that he didn't love her as much as he had loved Buffy. And no - it might not really mean that - but emotions, particularly such strong ones, are neither rational nor sensible. It would be a cause of jealousy and heartache, even if she was loved very much. Every day she would feel second best to Buffy (until the day she wasn't - and then he would kill her and everyone she cared about) even if she wasn't and that would eat away at her, it would destroy their relationship drip by drip. And that's if she even let it last that long because, let's face it, Cordy is not the kind of girl to walk around feeling like second best.
There is just no way this relationship could ever work.
Which isn't to say I specifically dislike the concept of CAngel; people fall in love with people they shouldn't do all the time so it's not that I think it's unrealistic they might fall in love with each other or that they might try to be together, because people do things that aren't sensible all the time as well ... but they can clearly never be endgame for all the reasons above. There's no marriage and babies and until death do us part here. It would definitely end and it might end badly, which would ruin everything they had had as friends. So I can't understand people for whom CAngel is OTP, because it is a terrible idea from start to finish. I can excuse Cordelia and Angel getting wrapped up in the emotion and throwing all caution and good sense to the wind (not that they ever do - it's a total non-starter) but I can't understand people thinking this is a good idea or wanting it to happen - beyond out of morbid curiosity or wanting to watch the tragic fall out.
I also never really understand where the substance worth shipping actually is in the execution (because it is executed terribly). Angel (and the audience) is informed he likes her in 'Offspring' but up until then ... there hasn't been anything to suggest it. Maybe one or two moments in hindsight (the bit where she announces she loves the Groosalug and he says 'but you love me too as a friend and coworker?...maybe love is too strong a word' ... I guess ) but it really does come - wham - out of the blue and doesn't even come from Angel himself. Cordelia doesn't know about it until 'Tomorrow' (where she is told by somebody else) and she effectively dies in that episode. The fact is - for all waiting in the wings is hot and heavy - she is written to be completely unmoved by the whole experience. So I'm a bit of a loss as to whether the shippers just ship the potential of the couple, or if they actually enjoy this walking disaster zone we get on the screen.
I also think people pull stuff from earlier seasons to support the ship, but it's not really evidence and it wasn't written as such and it requires an extreme (and often wilfully inaccurate) interpretation of the text. (And if you're leaning on Cordelia pre Halloween being into Angel then you are reaching - she's 16 and doesn't know he's a vampire, she shows no interest in him after that point. Angel was a hot boy she had a crush on, she didn't actually know anything about him and she got over him when she found out he wasn't what she thought.) I've had a CAngel shipper tell me there is evidence of CAngel in 'Eternity' because Cordelia looks sad when Wes explains to her how Angel can't find perfect happiness with just anyone and he won't find it with an actress ... that is not what is written and performed, it's an interpretation as viewed through extreme shipping goggles. I think people look for whatever evidence they can find because they like the friends to lovers trope, in general, and so are applying it to Cordy and Angel, rather than because their relationship has any merit as a romantic one in and of itself. If you like friends to lovers well - Cordy and Angel are friends, of course you would want to see them as lovers ... that much makes sense. It doesn't fit with what's on the screen, but it makes sense.
Unfortunately, Cordy and Angel ARE a hot mess as lovers. Both in execution and potential. If there was actually any mileage to the relationship, the writers would have put them together- even briefly. The fact that it's all missed opportunities and misunderstandings and hastily invented love triangles shows they just aren't capable of being believable lovers and a relationship would go nowhere, ultimately ending in a poor man's rehash of BAngel.
