"Free" contraception no more creates sluts than "free" food or "free" plastic spoons create gluttons. But they surely do enable those already so inclined as they no longer need to pay for their own consumables.
Of course, this is a novel use of the word "free."
I like to call it taxpayer-provided prevention of more welfare children with a corresponding decrease on social services, healthcare, and schooling that I would otherwise be paying for. So from that standpoint, the numbers pencil out.
Those who are most likely to to suck on the gov't teat and create more of same are not likely to make the effort to get even free birth control. Were talking some folks for whom cause & effect is akin to magic.
There needs to be:
1. Permanent/semi-permanent and reliable birth control solution.
2. Incentives for folks to partake.
I would place a bounty on vas deferens and fallopian tubes of, say, $2000 in gift cards. "Get cut, get cards." Maybe a $500 bounty on Norplant or similar long-term implanted birth control. "Get stuck, get stuff."