And what is your point?

Yes, taxes to pay for roads do indeed discourage economic activity.

This is a cost.

And the benefit that we get is the roads.

And in this case the benefits outweigh the costs.

But just because the benefits outweigh the cost doesn't mean that the cost doesn't exist.

And even people who don't drive consume goods that are distributed by trucks.

Correct. And?

Yes roads have benefits. They also have costs.

The benefits are greater than the costs, but we should be aware that the costs still exist.

If the benefits exceed the costs, it’s hardly fair to argue that the program slows economic activity.

Slowing economic activity IS the cost.

And the benefits outweigh the cost.

Yes. And when a program's benefits outweigh its costs, it seems weird to say that the program is a damper on economic activity.

In other words, if Option A is "get zero dollars", and Option B is "spend $1 to get $2", it is unfair to complain about B's "cost" (spending $1) in isolation.