Actually, this appears to be a pip upgrade issue.  If you install 3.6.5 from the python.org installers, there is no pip link there, only pip3:

$ cd /Library/Frameworks/Python.framework/Versions/3.6/bin
$ ls -l
total 272
lrwxr-xr-x  1 root  admin      8 Apr 16 19:19 2to3 -> 2to3-3.6
-rwxrwxr-x  1 root  admin    140 Mar 28 06:05 2to3-3.6
-rwxrwxr-x  1 root  admin    281 Apr 16 19:19 easy_install-3.6
lrwxr-xr-x  1 root  admin      7 Apr 16 19:19 idle3 -> idle3.6
-rwxrwxr-x  1 root  admin    138 Mar 28 06:05 idle3.6
-rwxrwxr-x  1 root  admin    253 Apr 16 19:19 pip3
-rwxrwxr-x  1 root  admin    253 Apr 16 19:19 pip3.6
lrwxr-xr-x  1 root  admin      8 Apr 16 19:19 pydoc3 -> pydoc3.6
-rwxrwxr-x  1 root  admin    123 Mar 28 06:05 pydoc3.6
lrwxr-xr-x  1 root  admin      9 Apr 16 19:19 python3 -> python3.6
lrwxr-xr-x  1 root  admin     12 Apr 16 19:19 python3-32 -> python3.6-32
lrwxr-xr-x  1 root  admin     16 Apr 16 19:19 python3-config -> python3.6-config
-rwxrwxr-x  2 root  admin  25920 Mar 28 06:05 python3.6
-rwxrwxr-x  1 root  admin  13568 Mar 28 06:05 python3.6-32
lrwxr-xr-x  1 root  admin     17 Apr 16 19:19 python3.6-config -> python3.6m-config
-rwxrwxr-x  2 root  admin  25920 Mar 28 06:05 python3.6m
-rwxrwxr-x  1 root  admin   2081 Mar 28 06:05 python3.6m-config
lrwxr-xr-x  1 root  admin     10 Apr 16 19:19 pyvenv -> pyvenv-3.6
-rwxrwxr-x  1 root  admin    480 Mar 28 06:05 pyvenv-3.6

But if you then upgrade to pip 10.0.0, which I'm guessing you did, you'll see:

$ ls -l
[...]
-rwxrwxr-x  1 root      admin    138 Mar 28 06:05 idle3.6
-rwxr-xr-x  1 sysadmin  admin    224 Apr 16 19:22 pip
-rwxr-xr-x  1 sysadmin  admin    224 Apr 16 19:22 pip3
-rwxr-xr-x  1 sysadmin  admin    224 Apr 16 19:22 pip3.6
lrwxr-xr-x  1 root      admin      8 Apr 16 19:19 pydoc3 -> pydoc3.6
[...]

So it appears the pip upgrade unconditionally installs both a pip and a pip3 link.  It really shouldn't.

You should check the pip issue tracker and, if not already reported, open a new issue there:  https://github.com/pypa/pip/issues/

Thanks for the report!