The whole reason people do Internet Marketing or Affiliate Marketing is because of the money simple as that.
I don't think I've ever met one person in all my 10+ years of doing IM/SEO that does it simply because they like doing it just for the sake of it.
They only like doing it when it brings in money. So in that respect, I love IM/SEO because it brings in money.
But I don't think anyone really truly likes spending hours and hours at their PC desk slogging away, doing SEO, writing articles, building links etc etc.
Everyone I've ever met that does it says they'd much rather spend their time with friends and family than on the PC all day.
Necessity? Well it's necessary to eat in order to live. So in that respect, it's necessary to put some food on the table, pay some bills and just have some extra money for rainy days.