Senior EM resident here, very happy with my job/life/career.
A few thoughts:
1. Look at the people who are telling you they are unhappy: were they happy in college? Med school? Residency? If you are a negative person then getting a long white coat doesn't magically change that.
2. Med school is hard, residency is hard, being a doc is hard. You know what else is hard? Subsistence farming, working in a sweatshop in Laos, fleeing war zones, or being kidnapped and sold into sexual slavery - hundreds of millions of people live like this right now as you sit in your AC'ed living room with your MacBook Pro. Get over yourself.
3. This loan/salary ratio stuff is such BS. You will make plenty of money. The people who cannot manage their loans on an attending salary would not manage their loans if you doubled their salary because they consistently spend more than they make. Understand that for the VAST majority of physicians this "hardship" is the difference between a 2011 BMW vs a 2008 Civic, not some more fundamental issue.
4. I don't know a single person who has had a relationship fail only because of their medical training. I am surrounded by people with happy marriages and lives outside of medicine.
5. If you want to spend your life looking for ways the world is out to get you, you will find them - no matter what career you chose.
6. If you want to use the fact that you work harder than your college friends who became engineers as an excuse to be an a**hole, go right ahead.
7. If you want to delude yourself into thinking that your college friends who now have desk/office jobs are in some nirvana of professional satisfaction, have a beer with them an ask them about it.
8. If you want to view medicine as a job instead of as a career, calling, and privilege you will be miserable.
Sorry for the rant but SDN is such toxic waste as far as these conversations go. Med students reading these forums probably get the idea that medicine is just terrible, nothing could be further from the truth.