Well, first, your friend was correct . . . not to answer the door . . . .it is just good practice . . . but, it could have been someone collecting for a charity . . . I still don't answer the door . . .
Second, I don't know where you live, but in Canada no one can come and arrest you for a bad debt unless you have embezzled a million dollars and only then can a duly appointed officer of the court (i.e. a police person) issue the warrant for arrest and that person will be dressed in officer clothing . . .
Perhaps, so you have a better range of vision, you need to install security lights that are motion detecting so whenever someone comes to the door you have a clear line of vision . . . ensure that you have a deadbolt lock on the door and you can see who is on the other side of the door before opening it and practice safe door answering . . . you are under no obligation to open your door to anyone (well, if the SWAT team shows up) even if they say they just need to use the phone . . .ask for the number and tell them that you will dial it and tell the other person the message . . . .
On the one hand, I do agree that you seem to have a bit of an overactive imagination, but, on the other hand, use it to your advantage and take an inventory of the security on your home and agree with your roommate on protocols for opening the door . . . it it is a stranger, don't even if it is a woman (I hate to say this, but, crime is an equal opportunity employer) . . . if it is an emergency and someone is hurt, dial 9-1-1 . . . . I am overly protective of my environment because I live alone . . . I do not think it is paranoid . . .now, I don't post sentry guards around my home, but I take due precautions . . . my next door neighbour parks his truck in my laneway, I don't leave the front door open even if I am on the main level, I lock up the garage because there is a door from the garage into the house, etc. No one can make a house a fortress (unless they are Bill Gates), but we can do due diligence . .. .so take precautions and then live your life . . .take care, KC