It should be noted, this is an SEO blog so while I will try to be as neutral as possible my opinions certainly lead toward SEO.

Compelling content is the name of the game.
You need to speak with the consumer, relate to them on the level they are at.  If they’re looking for a replacement blender chances are they’re not going to search for “replacement blender” but “my blender broke, what’s a good replacement”.  Marketing firms state that loading keywords into the content will put off the consumer and you will see your conversion rates tank.

One topic that often comes up is that search engine marketers load keywords and use their ‘tricks’ to manipulate the search engines for their own profit.  They will say that if all things were equal the website with the best content should and would always win out.

Optimizing for search brings the customers to you.
Compelling content may be higher converting but if you convert 90% of your visitors but if your total visitors is 100 a month versus 50% of 1,000 a month surely a lower conversion rate for a higher share is better.  The bottom line should be total conversions not percentages right?

Seeking out new developing niche markets can allow you to rank for new phrases quickly with good on-page optimization and thus driving more leads to your website.  You need optimized content to drive that traffic, then you can worry about converting.

My thoughts/conclusion: meeting in the middle.
Sure it might be a cop out to say meet in the middle but the reality is good news: you don’t have to compromise the copy much to rank well.  Too often search engine optimizers will get nailed down to a set philosophy.  We live and breathe numbers; whether it’s keyword density or number of incoming links.  We think in literals: we’re either optimized or we’re not.  And it doesn’t have to be that way.  All you need to do is be a little better than the guy at the top, have a little better link portfolio, and you can easily rank for the up and coming niche markets without butchering the content.

Content is king, but if it’s not seen it doesn’t matter.  However, you don’t have to compromise that content.  Maybe give a list of keyword phrases to the marketers and see if they can naturally slip them in.  Don’t get bogged down by keyword density.  Marketers, you are not diluting your final product by trying to fit in a few keywords the optimizers give you.  Your business is compelling copy, you are blessed with a wide vocabulary, surely you can fit in a few keywords where you think they fit.

Let’s face it, the marketers are here to stay and guess what, so are the search engine optimizers, so let’s find a way to work together.  Understand that the marketers probably know things you as an optimizer do not and vice versa.