为什么Python要使用有明显缺陷的引用计数而不是像JavaScript一样

这是一种设计取舍。用CPython的大家高兴就好呗。
其它Python实现有许多不用引用计数的，不高兴可以用它们（逃

另外CPython的引用计数是有mark-sweep备份的，不怕循环引用。
官网解释了这个选择（但其实也没说什么…）：https://docs.python.org/2/faq/design.html#how-does-python-manage-memory

The details of Python memory management depend on the implementation. The standard C implementation of Python uses reference counting to detect inaccessible objects, and another mechanism to collect reference cycles, periodically executing a cycle detection algorithm which looks for inaccessible cycles and deletes the objects involved. The gc module provides functions to perform a garbage collection, obtain debugging statistics, and tune the collector’s parameters.

In the absence of circularities and tracebacks, Python programs do not need to manage memory explicitly.

Why doesn’t Python use a more traditional garbage collection scheme? For one thing, this is not a C standard feature and hence it’s not portable. (Yes, we know about the Boehm GC library. It has bits of assembler code for most common platforms, not for all of them, and although it is mostly transparent, it isn’t completely transparent; patches are required to get Python to work with it.)
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Traditional GC also becomes a problem when Python is embedded into other applications. While in a standalone Python it’s fine to replace the standard malloc() and free() with versions provided by the GC library, an application embedding Python may want to have its own substitute for malloc() and free(), and may not want Python’s. Right now, Python works with anything that implements malloc() and free() properly.

然后请看这篇文章介绍较新的Python的“mark-swep GC”其实还是“分代式”的：http://patshaughnessy.net/2013/10/30/generational-gc-in-python-and-ruby

然后就是JavaScript也不一定是用mark-sweep的…语言规范没这么规定，实际实现也不全是用mark-sweep。

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