There are ways to monetize things even like a blog. If you create great content people will be attracted to your site. You can then use the traffic that you are drawing to sell ads to specific types of companies that align with your target audience.
It is important not to alienate your audience by putting up ads that are not relevant to them for two reasons. If you are putting relevant ads, it is actually a service to the people who are viewing your blog. If you are putting irrelevant ads it is going to make advertisers and your audience uninterested in your website. As you can tell, this simple act shoots you in the foot with two different sets of people.
Always take into consideration how it will affect your monetization.