There are other good things too. Political systems can only do a limited amount of stuff at once. They must prioritize.
Lowering involuntary taxes is one way to make the Government more voluntary and the people more free. It further would benefit the economy. But it can't be established just by wanting it. People have to work out how to change the budget to accommodate it. It takes quite a lot of effort, and in return there is a reward.
Simplifying the tax code is a good which would make it easier to feel good about paying one's taxes -- it helps it be more voluntary. It is also an economic good: it would save people time and effort. But it can't be done just by declaration. Knowledge has to be created about what changes to the tax code would not only simplify it but also retain the good aspects and not break anything.
We could focus on fixing social security. Or on how we fund education and what we ask of public schools. Or we could improve the health care system. Or we could reform welfare. Or we could change the military to use money more efficiently. All of those things would have economic and other benefits. And all of them are difficult. It takes a huge amount of effort to make serious changes to them. One has to plan out what to change, consider the effects it will have in detail, and persuade millions of people it's a good idea, including, generally, people from the other party (especially if, as one should, one hopes for a lasting improvement that can be stable to the other party being elected).
Which of these should be the highest priority? I don't know. But I do accept that there are a lot of factors involved. What we should not do is pick some principle, say freedom, and insist that whichever changes would most increase freedom must be the top priority. That would be thoroughly unreasonable.