As a Doc, who has only posted here once before... I can see there are arguments on both sides, but the lockdown side wins:
Yes, a travel ban may seem like shutting the stable door after the horse has bolted, but along with intense testing regimes, travel bans and lockdowns have been part of what has worked in the few countries who have got this under some sort of control.
The key issue however is that the number of deaths this will cause if there is, for example, a 70% world infection rate, is not fixed, but dependent on the capacity of Health Services to deal with the ill. If stopping cramming people into hot sweaty tubes of recycled air, less than 2m apart, for many hours, can help "flatten the curve" and keep health services functioning better, including functioning better for those who will fall ill with non-virus related conditions, such as Heart Attacks and multi-trauma, then it is a price worth paying. And the harder the lockdown, the shorter it will be.
Framing this in terms of rejection of environmental concerns, or interference with your Libertarian/free-market views is flawed logic. Any belief in yourself/your beliefs/your country being superior and exempt is misplaced. Above all, this is a time for people to show they do believe in helping and protecting others.
It amazes me that the avowedly Christian US politicians, have not yet understood the realities here, and connected them with their own moral compasses... Of course there is lots of brilliant work been done by believers, but they still voted for this transparently uncharitable man, whose approval rating has actually gone up recently!
Lastly; there may well come a time when - hopefully - mainland Europe and the UK are on top of all this, and infection is being managed in a sustainable way until a vaccine or treatment is available. I hope so. And at this point - on current evidence - I suspect it will still be out of control in the US, in Africa, and in the Indian Subcontinent. The WHO is already flagging the US as a future epicentre. Then, a travel ban on flights from the US to Europe may become very important.