Even though Macbeth says several good things about King Duncan, he never really directly states that he likes him. What he does, is to express as it is wont of a king's subjects, his gratitude, loyalty and subservience to his liege. These expressions do not necessarily come from the heart, but are spoken, as a rule, in terms of the requisite norms of courtesy and respect.
On being greeted by King Duncan and warmly congratulated and thanked for his courage and his service, Macbeth, for example says:
The service and the loyalty I owe,
In doing it, pays itself. Your highness' part
Is to receive our duties; and our duties
Are to your throne and state children and servants,
Which do but what they should, by doing every thing
Safe toward your love and honour.
Macbeth is saying exactly what he is expected to say. In the flattering language he uses here, he expresses the fact that rendering service, and being loyal to his king, is more than enough reward. The only requirement for King Duncan is to receive their service. The king's subjects owe duty to the king and his family. They, as the king's subjects, must do everything to protect their liege's love and defend his honour, and they would receive the same from him, when doing so.
The words Macbeth expresses here, are just that - mere words. By this time he has decided that King Duncan has to go and when the king announces that Malcolm should become Prince of Cumberland, Macbeth's intention is clearly expressed in an aside:
The Prince of Cumberland! that is a step
On which I must fall down, or else o'erleap,
For in my way it lies.
Macbeth believes that he has to overcome another hurdle in his plan to gain the crown.
In Scene 7, Act One, Macbeth mentions King Duncan's good qualities:
... this Duncan
Hath borne his faculties so meek, hath been
So clear in his great office, that his virtues
Will plead like angels, trumpet-tongued, against
The deep damnation of his taking-off;
And pity, like a naked new-born babe,
Striding the blast, or heaven's cherubim, horsed
Upon the sightless couriers of the air,
Shall blow the horrid deed in every eye,
That tears shall drown the wind.
The use of the word 'this' indicates the bitterness in Macbeth's tone. There is no love lost here. The word depersonalises Duncan and stresses Macbeth's resentment. He speaks of King Duncan's good qualities more as barriers to his success than as praise. He perceives the risk in killing Duncan. He was such a beloved and good king that his murder would overwhelm all his subjects with pity and everyone would soon know about the horrific crime. There would be such an outcry, that the many outpourings of grief would silence even the wind.
Macbeth has clearly hardened his heart and in this soliloquy he rationalises, in practical terms, what outcomes he should expect once Duncan has been murdered. This is therefore not an expression of his love and respect for his king, but rather his resentment of him and his fear for the consequences of Duncan's assassination.