While a layman uses the words Asura,Daitya ,Rakshasa synonymously but there are differences between them.
Atleast ,as far as a Daitya and a Rakshasa are concerned there is quite a good amount of differences between the two.
Manu Smriti, the oldest Dharma Shastra, describe everything in creation as manifestations of the 3 gunas(Triguna) viz-Sattva,Rajas and Tamas.
Each of these 3 groups are further divided into three more sub-groups viz-Sattva1,Sattva2 and Sattva3 where Sattva3 is the lowest form of Sattva and Sattva1 the highest.Similarly,there are 3 sub-groups each for the groups Rajas and Tamas.
Now,Manu describes the Rakshasas as the belonging to Tamas1.that is,the highest group among the Tamas category,where as a Daitya is said to be belonging to the group Sattva3,that is,the lowest sub-group belonging to Sattva.
12.41. But know this threefold course of transmigrations that depends on the (three) qualities (to be again) threefold, low, middling, and
high, according to the particular nature of the acts and of the
knowledge (of each man).
12.42. Immovable (beings), insects, both small and great, fishes, snakes, and tortoises, cattle and wild animals, are the lowest
conditions to which (the quality of) Darkness leads.
12.43. Elephants, horses, Sudras, and despicable barbarians, lions, tigers, and boars (are) the middling states, caused by (the quality
of) Darkness.
12.44. Karanas, Suparnas and hypocrites, Rakshasas and Pisakas (belong to) the highest (rank of) conditions among those produced by Darkness.
Here, darkness refers to tamas,goodness to sattva and activity to rajas.And highest rank of darkness refers to the group which i mentioned as Tamas1 and so on.
2.46. Kings and Kshatriyas, the domestic priests of kings, and those who delight in the warfare of disputations (constitute) the middling
(rank of the) states caused by Activity.
12.47. The Gandharvas, the Guhyakas, and the servants of the gods, likewise the Apsarases, (belong all to) the highest (rank of)
conditions produced by Activity.
12.48. Hermits, ascetics, Brahmanas, the crowds of the Vaimanika deities, the lunar mansions, and the Daityas (form) the first (and
lowest rank of the) existences caused by Goodness.
So,Rakshasa bound by his nature will act in the mode of darkness whereas a Daitya is quite similar to the Brahmins,the Ascetics etc in terms of inherent qualities.
So,needless to say,Daityas can be very righteous and religious but not the Rakshasas.
When the Devas and Rakshasas have a common hereditary lineage does behavioral leaning really set them apart?
In Manu's list the Devas are put in the Sattva2 sub-group,that is,just one group above the group the Daityas belong.
So,there are as much differences between a Deva and a Daitya as are implied by such a positioning.
12.49. Sacrificers, the sages, the gods, the Vedas, the heavenly lights, the years, the manes, and the Sadhyas (constitute) the second
order of existences, caused by Goodness.
Conclusion- A Rakshasa live in the mode of darkness(tamas) and their acts are often Adharmic.But a Daitya and Deva are almost on the same level as far as inherent qualities(Gunas) are concerned.In short,unrighteousness may be inherent by default in the Rakshasas but not so in the Daityas.
