> all taxes are simply put in a large pool
> I never support using taxation for social control
Yes, money is fungible, and so gas tax, alcohol tax, and cigarette taxes collected may not be applied to covering the costs of that activity. Even putting it in a specific fund doesn't completely fix the problem, it only establishes a minimum support for that fund's target. Make gas tax specifically fund road surface repairs, and then the DOT can use part of the general fund that is freed up for other purposes.
However, it seems very reasonable to use taxation as a sort of softer hammer to create an incentive or disincentive for various activities. In a way, the government's only power is in its monopoly on legal violence. It can do nothing but kill or imprison you by force. Sure, it can issue fines, or garnish your wages (effectively the same thing), or remove your drivers license, - but the fine has teeth only because they'll imprison you if you fail to pay. And if you try to fight your way out of captivity you'll either be pathetically overpowered or shot. Furthermore, criminal punishments require prosecution in a court, which is expensive and slow.
It would be unreasonable to try to reduce alcoholism by arresting people, charging them with drinking, and sentencing them with a $0.25 fine. It would also be unreasonable to pass a law requiring everyone to buy a house, get married and have 2.54 children, or be arrested and jailed.
Instead, taxation offers a much gentler stick, and sometimes even a carrot. Increase taxation on behavior that society finds to be objectionable or harmful - smoking, drinking, gambling, etc. Offer tax rebates for behaviors that society finds to be valuable: donating to charity, helping the environment, raising a family, owning a home. Taxation is definitely an effective tool for social control. Do you have an alternative? Or do you suggest that government should not be involved in social control?