Why Can't Good SEO Firms Use Cold Calling?

Recently, a member of a B2B networking site asked why cold-calling bySEO firms is considered a bad thing. I gave him a short answer, but thought others might be wondering the same, so decided to expand my answer into a full article.
I Googled the phrase "how to identify bad seo firms", and got over 209 million listings. Of the top twenty, two were obviously lead generation sites, and a few wrote about bad SEO techniques rather than bad SEO firms. Of those that addrerssed bad SEO firms, not one mentioned cold-calling as a way to identify them. And yet, I have seen articles on networking sites where otherwise knowledgeable people claim that it is. Why?
One rationale given is that website marketing firms that offer SEO should not have to use cold-calling - potential clients should come to them. This is almost treating the SEO industry as if it were a "Field Of Dreams" - "if you build it, they will come". I say "almost" because in addition to building it, the firm must also use their own techniques to get their website ranked for popular phrases related to SEO, so that when a potential client searches those phrases, they will find that firm. It goes without saying that a professional website marketing firm should be able to get their own site ranked, but why shouldn't they also actively pursue clients? To say they shouldn't almost seems self-aggrandizing - as if actively pursuing clients is beneath them, and that anyone who doesn't come looking for them is not important enough to bother with.
The other rationale is that sales representatives only sell their own programs, and know nothing about SEO. Isn't is possible that an SEO firm that gets it's website highly ranked can hire operators whose only job is to process phone orders? Not only is it possible, I'm sure it happens! What about those sales reps - they don't need to be experts, but what if the company provided ongoing training so they could at least have an intelligent conversation, and also provide access to professionals who can answer the questions the reps cannot?
The point is, the method of contacting potential clients is not the most important. The level of knowledge of the sales reps, and the people doing the actual SEO work, is what distinguishes a bad SEO firm from a good one.