kāmam āśhritya duṣhpūraṁ
dambha-māna-madānvitāḥ
mohād gṛihītvāsad-grāhān
pravartante ’śhuchi-vratāḥ
- Bhagavadgita 16:10
" Harboring insatiable lust, full of hypocrisy, pride and arrogance, the demoniac cling to their false tenets. Thus illusioned, they are attracted to the impermanent and work with impure resolve " said Krishna Paramatma in Geeta.
Paramatma said " lust, full of hypocrisy, pride and arrogance " are demonic qualities.
The question whether " were Devas always good and Asuras always evil " should be viewed in “ Reverse “.
People with good qualities are called Devas. Similarly people with bad qualities are called Asuras.
Suras mean Devas, naturally Asuras ( A + Suras - Not Suras) are those who are not Devas.
Subhamastu