I am not one. However I am married to one, and I just wanted to say that SPs can make a huge contribution to children's upbringing. Years ago as a single parent I was many classic things like failing to draw clear boundaries, and after taking a deep breath and trusting the woman who would later become my wife (who had a much more objective view of the situation, let's face it), things got far better.
I'm not going to drone on about it but we've just been on holiday and I was reflecting on it, and on the fact that good SPs rarely get the appreciation they deserve (or indeed any). So if you are one, give yourself a pat on the back. Or something.