Tell the truth.
Is it a good idea to the tell the truth?
Yes it is — always. Never lie, and never lie by omission either, by hiding details that you know are relevant to the situation.
Immigration officers are trained professionals who, by law, have to assume that foreign nationals have immigrant intent until they can show otherwise. They will immediately spot any cracks in your story and start digging, and any lies, however small, will instantly invalidate your credibility.
What is the purpose of your visit?
On top of that, you seem to be conflating purpose and timing. If they want to know why you want to go to the USA, "I want to be able to go whenever I want" is not an answer to the why, but the when.
You want to be able to go whenever you want - that's fine, why? What are you going to do once you're in the US?
Are there places that you want to visit as a tourist? Are you planning to work illegally on your tourist visa? Are you planning to overstay? Do you have enough ties to your home country that you're actually likely to go back before your visa expires? Do you have any friends or family members who already live in the US, that could potentially help you overstay?
Can you afford to live in the US for the duration of your planned stay (i.e., do you have enough money to support yourself)?
Also, definitely tell the truth, but if I may, adopt a more agreeable delivery: I don't feel like "I want to go wherever I want whenever I want" is an answer likely to be well received. It sounds defiant; I recommend that you avoid any behaviour or words which might be interpreted as defiant, arrogant or otherwise disrespectful or entitled.
For instance, you can say that because of the long wait times for interviews, the unpredictability of the worldwide Covid situation, etc, it is hard for you to schedule precise dates for traveling, but if at all possible, you would like to be ready to travel on short notice. You like to be prepared and have everything ready.
When going for an immigration interview, please remember at all times that you have no right whatsoever to enter the country you want to enter; an immigration officer has almost absolute power over the decision to grant you a visa, and if you lie (and they will catch you lying), they will probably do whatever they can to make sure that it's hard or impossible for you to try again.