Who are the "spacists"?

[Mikhail V]

So Python supports both spaces and tabs for indentation.

I just wonder, why not forbid spaces in the beginning of lines?
How would one come to the idea to use spaces for indentation at all?

Space is not even a control/format character, but a word separator.
And when editors will be proportional font based, indenting with
spaces will not make *any* sense so they are just annoyance.
Neither makes it sense in general case of text editing.
I think it would be a salvation to forbid spaces for indentation,
did such attemps take place?