Raise the Minimum Purchase Age for Tobacco?

Some lawmakers think this is a good idea:

Senate Majority Leader Mitch McConnell, R-Ky., announced he will introduce national legislation to raise the minimum age for people buying tobacco products from 18 to 21.

But evidence from the U.S. and elsewhere suggests the MPA-21 for alcohol has had minimal impact on drinking or driving fatalities among 18-20 year olds.  And rampant evasion teaches young adults that rules are made to be broken, thereby breeding disrespect for the law.

A MPA-21 for tobacco will suffer the same fate. Worse, it would be one more step down the slippery slope toward tobacco prohibition.  What could possibly go wrong?