First, for dealing with obfuscation and evasion, you're reading, not writing.
Second, for every 100 people that talk about e.g. self-modifying viruses or shellcode, there is perhaps 1 person who can actually write something soup-to-nuts, and maybe 5-10 more who can modify that code to make it do something new.
Reading assembly is important for security research. Writing, not as much.
