Imagine dating someone vs marrying. When you start dating you may be processing so many qualities but you don't take that long before you update your fb status. When you are getting married you are almost there with just one document to consider but you will take so much more time and effort, involve so many people (community, faith, law, family) before you are officially married. Turning off a bf/gf status (deporting a PR) is easy, not so much with the latter. So due diligence is required because you can't blame anyone else.
Ofcourse there are exceptions. If you claim asylum (get pregnant) and jump the hoop