"This just opened," a neighbor told me when my kids were toddlers as she stuffed a leaflet for a bilingual day care into my hands. "You should send them there." Day care is, for some reason, considered pretty important in my Eastern European country of residence — not just because it frees parents up to work, but also because people say it's important for small kids to spend time in "the collective" (the red specter still apparently lingers in the post-communist hive mind). My decision not to send my kids to day care was at times met with some interesting reactions; folks assumed, apparently, that it meant they never got to meet up with age peers and were bored all day.
This attitude toward day care is far from universal, and in other places, there are those who see parents who outsource a part of childcare as lazy, and their children as creatures to be pitied. I admit that I was, at times, quite amused by the comments the US "attachment parenting" gang shot mothers who sent their kids to day care. "Why have children if you're just going to pay other people to care for them?", was a common refrain. I've even heard digs along the lines of "you'll virtually be a stranger to your own child, just a person who tucks them in at night".
These mommy wars are really not cool, not least because those who engage in them usually seem to base their views on emotions rather than scientific evidence of any kind.
If your child is about to start attending day care, nursery, or preschool, and you feel even ever-so-slightly guilty, whether your day care plans are long-term or just for a season, here's why you should ditch your guilt. To add bonus points to your guilt-ditching, I — someone who never wanted to send her kids to day care but was guilt-tripped into it for three weeks anyway — will be your host for today. I'll have science to back me up, of course.
Organized childcare won't mess with the special bond you have with your child
Research shows that, while a child's primary caregiver — typically the mother — remains the child's main attachment figure when they enter an organized childcare setting, children do develop secondary bonds with caregivers in day care. The more positive your child's experience in day care, the stronger that bond will be.  This relationship doesn't take anything away from your special bond with your child. Rather, it just adds a new one! In other words, good-quality childcare in the context of a warm and loving family absolutely doesn't "cause attachment issues".
Day care won't affect your child's development negatively
I've seen the NICHD Study of Early Child Care and Youth Development used both to justify sending children to day care, and not doing so. That's precisely because the study concluded that "children who were cared for exclusively by their mothers did not develop differently than those who were also cared for by others".
The study also added that children benefit from growing up in families that offer them lots of intellectual stimulation in the form of play, books, and time spent outside, as well as that routines contributed to more positive outcomes. A day care center can, of course, play a role in providing these kinds of experiences. 
If your child's day care attendance makes you less stressed, it'll do the same for your child
Have you selected a day care setting in which you have total confidence — academically, philosophically, emotionally, and with safety in mind? Then your child's day care attendance probably will reduce your stress levels, no matter why they're there. Even if you'd rather not send your child to day care, but do so because you need to work, you'll rest easy knowing your child is in a nurturing, stimulating, and safe setting.
Now for some 'anecdata'
The parenting decisions I made when my children were small seemed to matter a whole lot at the time. The same was true for everyone in my "mom group", and we spent hours upon hours debating everything from how to give birth to whether to teach our little ones to read before they reached school age.
Most of my friends' kids — many of whom are still my kids' friends — went to day care. Some liked it, some didn't. Of those who didn't like it, some were pulled out and some went anyway. Of those who didn't go to day care, some had some extra trouble adjusting to school later on, while others fit right in.
The moral of the story? Well, there's absolutely no way to pick out which of these children attended day care and which didn't, as they enter their teen years. They're all thriving in their own unique ways, some extroverts, some introverts, . One of the day care kids still talks about her experience there fondly, however, so that's got to count for something.