By Serge Kreutz
This branch of Kreutz Ideology focuses on the pharmacological intervention with brain chemistry.
Basically, the human brain is laid out to react on sensual input and neuronal processing. It is not laid out for chemical manipulation. There even is a special blood-brain barrier to hinder it. 
Sensual input causes a wide range of physiological responses, from appetite for food to fear, from feeling cold to feeling lonely. Sensual input and neuronal processing also cause sexual desires, sexual arousal, sexual excitement, love, and jealousy. For young healthy men, pharmacological intervention is not needed.
But not all young men are sexually healthy, and even young sexually healthy men, unless they experience a premature death, grow older to an age when erections don’t work as well as in younger years, when sexual desire is lacking, and orgasms just don’t feel as overwhelming as they did. Ejaculation quality and fertility are also down.
1 Neuroscience For Kids, Neuroscience For Kids – blood brain barrier
2 Neuroscience Online, Blood Brain Barrier and Cerebral Metabolism
3 Amr Abdel Raheem, Philip Kell, Patient preference and satisfaction in erectile dysfunction therapy: a comparison of the three phosphodiesterase-5 inhibitors sildenafil, vardenafil and tadalafil , Patient Prefer Adherence. 2009; 3: 99-104.
4 Edward David Kim, MD, Erectile Dysfunction Medication: Phosphodiesterase-5 Enzyme Inhibitors, Vasodilators, Androgens , Medscape, Oct 12, 2015
5 Chelsea N McMahon, Christopher J Smith, Ridwan Shabsigh, Treating erectile dysfunction when PDE5 inhibitors fail, BMJ. 2006 Mar 11; 332(7541): 589 592.