Europe's humanist tradition is extremely precious and deserves protection. Everyone can freely worship under whatever superstition they choose, but it's important to recognize that Europe's humanist society is under threat.
That threat comes in the form of bloody religious madness, whose most prominent symbols include the burka and its derivatives. Not all Muslim women who wear the burka are forced to do so, but most women who lack personal freedom and agency are forced to wear it.
The burkini is a symbol of intolerance so contrary to Europe's humanist tradition, and so central to the purpose of those who seek to destroy that tradition, that it is justifiably banned. Freedom of expression is not unlimited, neither in Europe nor in the US, nor should it be.
Women who benefit from all that Europe's humanist tradition provides, can make a minor sartorial concession in the exercise of their superstitions, in order to help protect, and show their commitment to, the society in which they chose to live.