kontera is a company that puts random text link ads on your site, you can sign up with them. you install a code and random words will periodically light up with a link to an advertiser. i removed Kontera when I hovered over the word "baby" and it said "Buy Baby Here. Baby On Sale."
there are also companies who will pay you to talk about their website or company. You can hook up with them through payperclick or smorty, and several other agencies that connect bloggers and companies.
I don't think it's bad unless you suck at it. And I'm not saying I don't suck at it either. They don't tell you what to write, they don't force you to say nice things. If the site completely sucks and you want to say that, you can.
I try not to write about things that are irrelevant to my site. I did a few insurance ones and it was just strange. I would never talk about insurance kindly in real life.
I look at it as a creative writing exercise. I don't think it's wrong, I think it's silly to think it's wrong. My blog has a disclosure policy posted. I wouldn't send traffic to a site that I thought would be harmful to people. How harmful can a site be, though? Honestly, this is the Internet and we're mostly all adults here.
Google adsense is popular, too.
It's not just money to be made, I've gotten free products to write about, too. I don't think it's a big deal, I write about products anyways, when I have something to say.
There are other opportunities to be had in blogging, but my traffic isn't big enough for some of them. Mostly, I use my blog to communicate with family and friends, remember things my kids do, and direct people to my work on other websites.