I agree with some posts here, and I'll give my two cents.
I think, that if both participants are above age, say, 16, and the guy has a decent job at that point, and can support the consequences of having a child, or in a worst case, more than one child, then I see no reason as to why it would be bad.
This is also a huge reason behind everything. Most guys who look for sexual relations before age 20+ generally don't have a job, and don't care, they're just looking for a good time. If that's the case, then yea, it could be bad.
I just think that if you're MATURE enough to handle it, then it's nobody else's business what you do with your life. But, like I said, I'd estimate that 70% of guys, or girls aged anywhere from 15-19 aren't necessarily ready for bad consequences, seeing as the guy probably doesn't have a job, and probably doesn't want to support a family.