1 (b)

aller-: very (single most)
nützlich: useful (handy, valuable, utilitarian, advantageous) 
die Hinsicht: regard (respect)
sich unterhalten: to chat, to chatter, to converse, to confer
die Wirkung: impact, effect, virture (appeal, force, consequence)
der Trieb: urge, instinct, desire (shoot, sprout, drive (psych)) 
längst: long since, long ago

erschlaffen: to slacken (to go limp)

verfaulen: to rot (to decay, to fester)

der Raub: robbery (heist, rape, deprivation, predation)
die Herrschsucht: imperiousness (bossiness, domineering nature)
nennen: to mention, to name, to call (to dub, to state)
erstaunlich: amazing, astonishing (marvelous, admirable, astounding)
die Arterhaltung: conservation (or preservation) of the species
freilich: "True,...",certainly, admittedly (however, of course) 
kostspielig: costly, expensive (pricey, sumptuous)
verschwenderisch: lavish, wasteful (profligate, luxurious, prodigal) 
töricht: foolish, silly, fatuous (asinine)
bewiesenermaßen: to prove (s.t)  *not in dict.cc, but other online sources point to this and er- rather than be- prefix is translated on dict to be "prove or evidentially" 
das Geschlecht: gender (sex, house, species, race)
bisher: yet (hitherto, heretofore)
erhalten: to obtain, to receive, to maintain (to get, preserve, retain, gain)

Auch der schädlichste Mensch ist vielleicht immer noch der allernützlichste, in Hinsicht auf die Erhaltung der Art; denn er unterhält bei sich oder, durch seine Wirkung, bei andern Triebe, ohne welche die Menschheit längst erschlafft oder verfault wäre.  Der Haß, die Schadenfreude, die Raub- und Herrschsucht und was alles sonst böse gennant wird: es gehört zu der erstaunlichen Ökonomie der Arterhaltung, freilich zu einer kostspieligen, verschwenderischen und im ganzen höchst törichten Ökonomie--welche aber bewiesenermaßen unser Geschlecht bisher erhalten hat. 

Even the most harmful man may really be the most useful when it comes to the preservation of the species; for he nurtures either in himself or in others, through his effects, instincts without which humanity would long have become feeble or rotten. Hatred, the mischievous delight in the misfortunes of others, the lust to rob and dominate, and whatever else is called evil belongs to the most amazing economy of the preservation of the species.  To be sure, this economy is not afraid of high prices, of squandering, and it is on the whole extremely foolish.  Still it is proven that it has preserved our race so far. 

Even the most harmful person may actually be the most useful when it comes to the preservation of the species; for he nurtures in himself or through his effects on others drives without which humanity would long since have become feeble or rotten. Hatred, delight in the misfortunes of others, the lust to rob and rule, and whatever else is called evil: all belong to the amazing economy of the preservation of the species, an economy which is certainly costly, wasteful, and on the whole most foolish--but still proven to have preserved our race so far.