That's a very simplified observation of a complex reality. Not all daycares are created equal: The National Institute of Child Health Development[1] found that most daycare operations are "fair" or "poor". Only 10% are "high-quality". Obviously the details are what matter in each case: a caring parent at home is far better than a crowded day-care. Conversely, a great daycare can help with a bad home situation.
[1] https://www.nichd.nih.gov/publications/pubs/documents/seccyd...
Most children in Sweden have two working parents and start daycare when they are around a year old. Daycare in Sweden is considered part of the school system and the teachers working there have (approximately) the same education as 'regular' school teachers.
Edit: Also, as a related fact in this discussion, in Sweden children that are behind in learning to speak (language development) can actually receive special permission to spend _more_ time in daycare to help speed up their language learning.
There is certainly more to a child's behavior than whether their parents were working or staying at home. There might be a strong correlation to households with two working parents and households with other developmentally-stunting factors like parental illiteracy or low education levels, low levels of parental involvement, etc, but I'm sure you would have a tough time proving to any level that, with all other factors remaining the same, two working parents cause more damage to a child than having a stay-at-home parent.
For what it's worth (as long as your anecdotal experience means something to you), my brother-in-law is a college administrator and my sister is a first grade teacher and they have two children who don't seem to have any developmental issues. But my sister has kids in her class with a stay-at-home parent who certainly do.
One relevant source: http://www.ncbi.nlm.nih.gov/pubmed/17381797
Yes, this can be done by taking the kid to a park or other social activities, but two working parents is a perfectly acceptable option too. Daycare isn't unbeneficial to a child.