There are only a couple considerations here: first, they do force you to pay this in any case or you can't do business at all. The rationale is that having health insurance / social security is not optional in Spain. Thus the illegality of doing business / working without paying that. I would leave this untouched.
The other consideration is that you have to pay this even if you have a salaried job and your employer is already collecting from your salary and doing the contributions for you. I would make it unnecessary to pay the extra 250 EUR/month in this case, it doesn't make sense, except for people with very low salary (for whom no social contribution is mandated for their employer), in which case I would keep the need of contributing separately, or it's a huge loophole to avoid contributing.
A socially-oriented state has some cost, you know. Having to pay 250 EUR/month when you do business is such a ridiculously low price to pay for near-universal health care.
