It seems to me that it would be wrong to ban testing on animals for vital medical research until equally effective alternatives have been developed.
问题1:为什么这里用it would be，可以直接用 it is吗？假如可以的话，不同在什么地方呢？
问题2:为什么这里用have been done，个人感觉整个句子说的并非过去。
请各位老师帮忙解惑
it would be wrong to ban testing on animals for vital medical research until equally effective alternatives have been developed.
这是一个含蓄虚拟条件句。不定式表示的事件在说话人看来是不会发生的。虽然不定式做的是主语，但它隐含假设意义：If the government were to ban..., it would be wrong.
until引导的时间状语从句表示的是以后可能的事实，为陈述语气。时间状语从句用目前完成年代替以后完成进行时，这是你在中学应该学过的内容。这并非表示过去。
