Prior to Vatican II, Protestants frequently were conditionally baptised. Also, most Protestant sects save for the Lutherans and maybe the Anglo-Catholics deny that Baptism is for the remission of sins and DO NOT have the Church's intent for baptism. Even if they have the proper form, they lack the proper intention.
Liberalism does not change the objective invalidity of Protestant "sacraments".
My Melkite pastor always rebaptises Protestant converts.