Why go on birth control

I have extremely irregular periods, I miss months upon months. But I do an extreme amount of excerise, long distance running, lifting, etc. I never felt I needed to go on birth control to regulate because it was considered normal when you're an athlete. However, my boyfriend and I do enjoy not using condoms. I do plan on going on birth control but is it wrong to solely want to go on it so we can be more safe having sex and he can finish in me (Instead of period regulating even if mine are irregular). We are older, and stable to be able to have a child if we had to do that.