The replies given above are right on the mark . . . . . . however, I feel that the essence of the problem may be in the incorrect rendering of the verb tenses.
Taiwan is not currently under the administrative control of China. Foreign visitors (for example) who want to come to Taiwan cannot apply for relevant visas from China’s overseas Embassies. Taiwanese citizens pay no taxes to China, nor do Taiwanese males serve in the Chinese armed forces.
Hence, I believe it is more correct to say that the One China Policy may indeed reflect the international consensus that Taiwan will become a part of China, although at some undetermined date in the future.
I repeat that at the present time, Taiwan is not a part of China, legally anyway.
Therefore, if we accept the reality that Taiwan is Taiwan, and China is China, it seems that the One China Policy is a fair policy. Well, that is the way I read it . . . . . . and additionally, I note that no one in Taiwan has the authority to change this One China Policy . . . . . . so they had better get used to it, and/or find a way to conduct their lives within its parameters.
Again, I believe the way out of this problem is to stress that Taiwan is Taiwan.