In my own research, I've explored the "damned if you don't" aspects.
A popular misperception about singlism is that it is only targeted at singles who have passed a certain age -- maybe mid-30s.
Everyday brushes with mild versions of matrimania could include exposure to stereotypically romantic images, or overhearing people discussing their dates in a context that is supposed to be about research and scholarship.
This deepening depression occurred even for those who got involved and stayed involved -- so the findings were not simply a matter of feeling badly about a break-up. Depression among the romantically involved increased for both the males and the females, but it increased more for the females. The increase in depression among the romantically involved was also especially great for those adolescents who reported attraction to people of the same sex and for those who reported no romantic attraction toward either sex. Both the males and the females who became romantically involved reported more problems with drinking and delinquency than did their peers who were not romantically involved.
From that perspective, 20-something singles are not viewed any more harshly than 20-something couples or married people.
Wendy Morris and I have looked into that, and we found that the stereotyping really is harsher with regard to 40-year old singles than 25-year olds.
(I described more of the details of the research, including the authors' speculations as to why romance might be linked to such vulnerabilities, in this post and this one from my "Living Single" blog.) Another study of more than 1,000 Spanish adolescents examined the link between romantic experience and sexist attitudes.
The authors found that the males with more romantic experience were more likely than those without such experience to endorse beliefs indicative of "benevolent sexism." Benevolently sexist attitudes seem superficially positive, but can actually be patronizing -- for example, "Women should be cherished and protected by men." In contrast, the females with more romantic experience were more likely to endorse attitudes of "hostile sexism." That variety of sexism is typically directed at women who don't stay in their place.