Being a parent is hard work. If you're doing it alone and doing a good job, as many do, then fair enough on feeling proud.
People fall into such situations for many reasons, some entirely in their control, some partly in their control, many not in their control at all. Given the huge number of failed marriages, split parenting, blended families, it seems a little harsh to look down our noses at those who, for whatever reason, are doing it alone.
Facebook memes are almost always **** though. Don't confuse your, rightful, indignation with those for actually being upset with the group of people incorporated into them.
E:
Aren't you gay anyway, OP? might that affect your understanding of the attraction of single mothers?
I could see myself happily hooking up with a single mother if I was to end up single again. But, then, I'm married to a woman with kids (my kids), so the prospect doesn't seem all that alien.