I have three kids, ages 5 and under, and this is what I think:
First off, we do not CIO with our kids. I definately do not think that you HAVE to let them scream. I also really really disagree with the opinion that your baby is trying to manipulate you. It's a baby, not an evil genius. Their little minds are just not capable for manipulation yet, IMO. The only tool they have is crying when it comes to having needs met, kwim? I personally don't feel as though there needs to be an "us against them" mentality. Now, with my first kid, I thought CIO was cruel and awful. I have mellowed a ton since then and fallen off many a high horse. Never say you'll never do anything once you have kids.
I just didn't put "sleeping through the night" at the top of my priority list for my kids. They are all different, too. My youngest is almost 6 months old and practically there. My middle was closer to 2. My first was somewhere between that. So my worst case scenerio was 2 years. And you know what? 2 years just isn't that long in the grand scheme of things. This is what I truly believe: Some kids are bottle fed, some are breast fed. Some CIO, some cosleep, some fall somewhere between the two. Some kids have moms that work, some have working moms. Whatever. When they are 6 years old they'll all just be a bunch of 1st graders. No one will be able to tell who slept through the night first or who was breastfed or blahblahblah. So, if sleeping through the night is your top priority and if you feel comfortable doing CIO, go for it. The kid will be fine and there's nothing in the world for you to feel guilty about. If you aren't comfortable with it, then don't do it. Period. Because whoever said it is right, mom knows best. And that's you.