I'd say Romania is actually relatively safe crime-wise for tourists. Comms services are better than in my homecountry (always had 4G on my last trip to Romania even in rural places in the mountains, while I sometimes do not have any signal in German high-speed trains between two large cities). Dangerous widlife is actually an issue. Lot's of bears, wolfes, snakes, etc. Also bad tourist infrastructure in really rural places.

Nothing. Romania is generally fine. I hitchhiked an couch surfed solo. Had only good experiences.

No problem, its not some golden rule you should follow (especially from an internet stranger) but it's mainly bad roads, bad economy (poor police/ambulance availability), the little Roma villages/gipsy makeshift living areas, where I would not show up alone with any valuables (similar to gipsy ghettos near big cities) and last but not least wildlife. While bears and other predators are not uncommon, rabid dogs are also a possibility.

Before somebody accuses me hating Romania (its a beautiful country with incredible landscapes and the capital and developed parts are very popular tourist destinations), the above is also applicable for many other europen countries. This is why I strongly suggest doing some research before planning such trips, as the relative safety and enjoyment of a holiday can vary from region to region within a small country. This is why its borderline impossible to give a straight answer to the original post.

Nothing happens to them because all the bad parts of Romania aren't in places where backpackers would go. Only "bad" part of visiting Romania is that tourism isn't as developed as in other countries. So not as many signs/information/buses to and from places. That also makes lots of places harder to find and reach but also a lot more pristine. Romania's countryside is one of the best, hands down.