Is there a general summary of the arguments made by the dissenting 4?
Don't get the tl;dr summary of Scalia's dissent; actually read it. Scalia is obnoxious and mean-spirited (and in fine form this time), but he's a really good writer, the fun- to- read kind. IIRC, he wrote a book on writing with Brian Garner, of usage dictionary fame.
"The real rationale of today’s opinion, whatever disappearing trail of its legalistic argle-bargle one chooses to follow, is that DOMA is motivated by ‘bare … desire to harm’ couples in same-sex marriages. How easy it is, indeed how inevitable, to reach the same conclusion with regard to state laws denying same-sex couples marital status" (Windsor, J. Scalia, dissenting).
“[W]hat justification could there possibly be for denying the benefits of marriage to homosexual couples exercising ‘the liberty protected by the Constitution’? Surely not the encouragement of procreation, since the sterile and the elderly are allowed to marry.” (Lawrence, J. Scalia, dissenting).
Roberts also argued Scalia's own logic back at him in this week's decision upholding the ACA, noting that in 2012 in the decision upholding the requirement to buy health insurance Scalia had stated in his dissent that without the subsidies (for low income insurance buyers), "the exchanges would not operate as Congress intended" because health insurance would be too expensive for low-income taxpayers.