Marriage guarantees nothing. Avoiding marriage guarantees a (very) few things, but some of which have real value, such as never being the victim of a divorce lawyer. Some of the things marriage brings are not consequences of the marriage, but of despicable, coercive force: if you aren't married, you may not be allowed to see someone you care about who is in extremis. You may not be allowed to take care of their obligations for them if they are sick.
1) depending on the relationship, you might still wind up needing to see a lawyer. I can imagine an unmarried man in this environment having zero presumed(?) rights to his own children in the eyes of a judge. How do you split a house or other large, shared assets? A smart couple will set these things in writing before things go bad, but not everyone has the foresight.
2) Not having visitation/decision-making authority is a real problem for non-married couples and can't be overstated enough. Before gay marriage was legal, a friend of ours had emergency surgery and his boyfriend was not allowed to visit him in the hospital. So my girlfriend and I got the paperwork taken care of. It was expensive, but worth it. For anyone interested, visitation and decision-making do not have to go hand-in hand. One feature about being unmarried is that you have to specify exactly what rights your significant other should have and under what conditions. Marriage basically grants root access by default
I strongly encourage anyone in a positive, long-term relationship who isn't planning on marriage to see a family lawyer and get the right paperwork in place (advanced health care directive, wills, trusts, etc). If you have any meaningful assets (house, retirement account, rainy-day fund, etc), maybe talk to an accountant about minimizing tax burden on your significant other after your death. But a little bit of paperwork and morbid thinking now will save you or your partner a lot of pain later.