If we're talking about the negatives of marriage for women, I'm not sure I'd include cohabitation. Simply because even though marriage can be argued to 'trap' women, it also offers some protection in the event of relationship breakdown that isn't there for a woman living in a cohabiting relationship that fails. Of course, it's possible to enshrine all those benefits through legal means without getting married, but few people seem to do so and with rare exceptions it seems to be nearly always the woman who falls foul of it.
Not that that's an argument to get married, but in terms of the OP it's why I wouldn't necessarily lump in marriage and cohabitation in the same group.
In terms of daily life, I agree that there probably isn't much difference though. Legally marriage is a big deal, but it doesn't make any difference to how you live that marriage.
Do I think both suck? For a lot of women, sadly I think it does. I know several people who are happily married and for whom the benefits are obvious. Neither party in the relationship would be able to do what they do as a single person and both would experience a significant drop in income should they separate. Their respective families have become a united whole and, of course, perhaps most importantly 
they love each other. They represent the idealised (modern) notion of marriage and how it should work. And for couples like this, it does work.
However, I don't believe that's the reality for the majority. Given the rate of relationship breakdown (combining divorce and cohabitation breakdown) the rate is about half. Of the remaining half, are they all happy? Of course, they're not. We all know people who are miserable together, or whose spouse is having an affair. THen you have domestic violence at a rate of 1 in 4. For me, the only conclusion is that for most women, marriage and cohabitation does not equate to happiness, love, fidelity, bodily integrity and respect. Factor in the research on poverty, which shows most women still earning less than men and much more likely to be poor - particularly on relationship breakdown which ^does not affect the man in the same way nor to anywhere near the same extent - and it's clear that marriage and cohabitation do not equal financial stability either unless you stick at it through thick and thin despite all else (including infidelity and abuse). To me, that seems to be the definition of 'trapped'.
I think marriage is a by-product of a different age, when society was organised on different lines. I don't think you can look at it without taking into account its cultural backdrop. Of course, it has changed over time. The over-riding reason for marriage now is love, whereas not so long ago that was probably at the bottom of the list of reasons to get married, when it was all about property union. That doesn't mean that all of the effects of those original purposes for marriage have vanished though. Women remain more likely to be raped and assaulted by their marriage partner than they do a random person on the street, they are still more likely to be the secondary earner and so more vulnerable.
Do I judge individual women for getting married? Of course not. Like I said, when marriage does work for both partners, it can work exceptionally well. It's a cornerstone of our culture and the building block of society. It's normal and as such it would be crazy to judge individual women for making a normal decision - especially if they are one for whom it does actually work quite well. However, that doesn't stop me from thinking that, generally speaking, marriage hurts more women than it protects and is only one way of organising your life. If there was a true choice in how we live our lives (e.g. no one batted an eyelid at other choices and our economy was geared up to different types of household rather than the heterosexual pair bond) I think we'd see a lot more variety and have a much nicer society. I think we'd find a lot more same-sex platonic households in which sex was something that happened in a relationship but not a cohabiting/married one. We'd still have married couples, but we'd have variety, and personally I think that would be a good thing and provide much greater stability for a lot of children.