SB 11.28.2

para-svabhāva-karmāṇi
 yaḥ praśaṁsati nindati
sa āśu bhraśyate svārthād
 asaty abhiniveśataḥ
Synonyms: 
para — another’s; svabhāva — personality; karmāṇi — and work; yaḥ — who; praśaṁsati — praises; nindati — criticizes; saḥ — he; āśu — quickly; bhraśyate — falls down; sva-arthāt — from his own interest; asati — in unreality; abhiniveśataḥ — because of becoming entangled.
Translation: 
Whoever indulges in praising or criticizing the qualities and behavior of others will quickly become deviated from his own best interest by his entanglement in illusory dualities.
Purport: 

A conditioned soul desires to lord it over material nature and thus criticizes another conditioned soul whom he considers inferior. Similarly, one praises a superior materialist because one aspires to that superior position, in which one may dominate others. Praising and criticizing other materialistic people are thus directly or indirectly based on envy of other living entities and cause one to fall down from sva-artha, one’s real self-interest, Kṛṣṇa consciousness.

The words asaty abhiniveśataḥ, “by absorption in the temporary, or unreal,” indicate that one should not adopt a concept of material duality and praise or criticize other materialistic persons. Rather, one should praise the pure devotees of the Supreme Lord and criticize the mentality of rebellion against the Personality of Godhead, by which one becomes a nondevotee. One should not criticize a low-class materialist, thinking that a high-class materialist is nice. In other words, one should distinguish between the material and the spiritual and should not become absorbed in good and bad on the material platform. For example, an honest citizen distinguishes between the life of civil freedom and that of imprisonment, whereas a foolish prisoner distinguishes between comfortable and uncomfortable prison cells. Just as for a free citizen any situation in prison is unacceptable, for a liberated, Kṛṣṇa conscious devotee any material position is unappealing.

Śrīla Bhaktisiddhānta Sarasvatī Ṭhākura indicates that rather than trying to separate conditioned souls by materialistic distinctions, one should bring them together to chant the holy names of the Lord and propagate the saṅkīrtana movement of Lord Caitanya. A nondevotee, or even an envious third-class devotee, is not interested in uniting people on the platform of love of Godhead. Instead he unnecessarily separates them by emphasizing material distinctions like “communist,” “capitalist,” “black,” “white,” “rich,” “poor,” “liberal,” “conservative” and so on. Material life is always imperfect, full of ignorance and disappointing in the end. Rather than praising and criticizing the high and low features of ignorance, one should be absorbed in Kṛṣṇa consciousness, on the spiritual platform of eternity, bliss and knowledge.