I'm using the common idiom, I don't think it's actually evil but in my opinion it's definitely a fundamentally negative practice that is unfortunately required to be used in the process of doing something otherwise positive. Servers and programmers aren't free, and if what you're doing is positive then you're still socially net positive despite the negative impact of advertising.

I'm not saying that all advertising is bad either, it's the specific case of B2C online advertising that compromises privacy and massively reduces the signal:noise ratio of the platform you're using. Sales and marketing aren't inherently bad in themselves, obviously.