Is it a bad idea to get pregnant on purpose?

Do both want baby? Women and their partners should discuss if they are ready to assume the risk of pregnancy and the responsibility of raising a child. If so, there should be a visit for general exam and discussion of health histories (of both and families) by gyn doctor, avoidance of toxins, adherence to balanced healthful diet and to taking appropriate vitamins, whatever else the doctor advises for both partners, .
No! Planning a pregnancy gives you the opportunity to make sure you are as healthy as possible before you get pregnant. Having a consultation with your doctor beforehand gives you the opportunity to address any medical issues that could be optimized. This gives you the best chance at having a healthy outcome for both mom and the baby.
Proceed with caution. Are you getting pregnant on purpose to keep a relationship/ increase the size of your family? Many women purposely get pregnant with thoughts that their partners will stay and help support them and the baby. Doesn't always work. Evaluate the relationship first before going down that road... Which ever you choose. You may end up with a responsibility you may not be able to handle alone.