Specifically, using tabs to align defeats the purpose of using tabs. (You are no longer free to choose your preferred indentation distance)

Using spaces to indent, on the other hand, is a bit like having a fixed width web page. It is the wrong size for the majority of people, but it is at least consistent.

In a perfect world, everything would show tabs at your preferred width, people would not use tabs for alignment and everybody would see code in their own preferred style independent of the original coder. Indentation would be distinct from code. There could even be a way to indicate which curly brackets qualify for an optional linebreak plus indentation.

But display/edit programs don't show properly, and people don't write properly. This is why we can't have nice things :P

PS: Actually, this seems a lot like web pages... using tabs to align is as bad as using a 20% width object to align text. Just Doesn't Work.

Using spaces everywhere is like perldoc's fixed width syndrome. Running a script to convert the indentation (bigger or smaller) is like having to write and apply a style override for the website. Makes it less convenient and uglier than it should be, but also more useful than the original state.