But you have to Admit Phil "give their love unconditionally" and "forcibly evolved" paint two different pictures.
I don't think they do, Malc : the animal (pet) has been forcibly evolved to give its love unconditionally. It has no choice in its selectively-bred inherited traits, and having inherited those traits, it has no choice (or very little choice) other than to behave in the manner for which its genes code.
Returning to your earlier point, "I wonder if the so called pet would remain so loyal if you stopped feeding it and opened the door", I would offer two observations : (1) After a short period (a few days at most in cats, much longer in dogs), the animal would leave. (2) But except in very rare circumstances it would not then elect to go feral : rather, it would seek out another human who could offer love, food and accommodation.
I share my home with a 3-legged cat "Jaffa", who adopted us about 14 months ago. His former home is within less than 100 yards (probably closer to 50), and he returns there from time to time, mainly (I think) to seek out his brother, with whom he remains close even at the age of 13 (I cut a cat-flap-shaped hole in the intervening fence to facilitate his excursions). But when I went away to Abu Dhabi for a few days, despite making arrangements with three separate people to come in and feed him and attend to him, within two days he had returned to his former home, and there he stayed until my return. One rather sad thing is that he almost certainly suffered some brain damage when he haemorrhaged after surgery (he crashed twice, and needed three transfusions), and when he goes upstairs late evening, he then cries to be let into the closed bedrooms : he almost certainly expects to find his brother there (which is where he would be in his former home), and he is clearly sad and disturbed at not finding Tumble there ...
** Phil.