I don't even do it on purpose and it's rarely with malice. Nevertheless, I do it too.
If I didn't unintentionally judge, then I wouldn't constantly think that I'm screwing up somehow. Every time I blog or chat with a friend, I wouldn't think to myself, "do they think I'm doing it wrong?" Or "am I totally going to ruin my kids".
On subject matters like, breastfeeding (the bane of my existence), crying it out, watching TV or making homemade baby food. Once, I told a friend of mine that she was an over achiever because she made her own baby food. What? Was that even necessary? It was actually a compliment but did it come off as snarky, probably.
None of us actually, really know what we are doing. If you claim that you do, you're full of shit and should stop reading my blog immediately. There are plenty of different routes to take to raise kids, and for the majority, we are all trying to raise them well.
Even to parents and grandparents whose children are already grown, I bet there are things they wish they'd done differently but everything was done out of love and the best of intentions. No point in regrets. Does that stop them from judging? Nope.
I read several mommy blogs (Terrilox, Scary Mommy, Momtastic) and it's such a common theme. We beat ourselves up over what we think others are thinking! OMG! No más!!
So going forward, every time I see someone doing something we don't, i.e., bumpers/pillows in a crib or babies/tots watching TV, I'm going to refrain from thinking anything other than "look how cute that kiddo is!" Hopefully the kid is cute. :)