The amount of comments espousing the idea that stable marriages can't be happy is off-putting to me and what I see as a reflection of how Americans value marriage.
Your post, and the upvotes it's getting, are the second wave :)
HN commenters (or the stereotype thereof) who are married would actually be more likely to be in stable marriages, and thus able to weigh first-hand the relative likelihood of a stable/happy correlation.
I don't see anyone saying this. Instead the claim is: when divorce is a cultural taboo, people are more likely to stick in an unhappy or even abusive marriage. This claim seems pretty uncontroversial, but at any rate it is a positive claim (not normative) whose accuracy can be judged by empirical data.
I'm less sure of evidence that cultural taboos have the same effect. Here's some correlational work across countries on divorce norms and gender equality within marriage; this doesn't specifically address violence, though, and it doesn't control for other aspects of culture which probably covary with attitudes to divorce [4].
[1] Stevenson, B. and Wolfers, J., 2006. Bargaining in the shadow of the law: Divorce laws and family distress. The Quarterly Journal of Economics, 121(1), pp.267-288.
[2] Gruber, J., 2004. Is making divorce easier bad for children? The long-run implications of unilateral divorce. Journal of Labor Economics, 22(4), pp.799-833.
[3] Wolfers, J., 2006. Did unilateral divorce laws raise divorce rates? A reconciliation and new results. American Economic Review, 96(5), pp.1802-1820.
[4] Yodanis, C., 2005. Divorce culture and marital gender equality: A cross-national study. Gender & society, 19(5), pp.644-659.
Immigrants can come from anywhere, and different countries have different views on divorce. Some countries are much less strict than the US on this matter.