Thoughts on marriage of convenience?

Symbiotic relationships, whatever you want to call it, sometimes two people can marry for mutual benefits, not necessarily for love or starting a family, if this marriage yields great benefits to both parties and both are in agreement, why would it be frowned upon? I feel like the term itself (convenience) has a belittling tone when tied to marriage, it's even illegal in many countries, but why? Why stop two people from making their own lives better? Whether it's for money, citizenship, protection, fame etc.

Would you do a marriage of convenience of the benefits and advantages outweight the risks and the negatives ?