The problem isn't using one consistently, in self-written code, but students will copypaste small snippets from somewhere. While python recommends using spaces for everything, more than enough code exists that uses tabs. Now; not every IDE is smart enough to actually convert everything to whatever is set. It may work for PyCharm or VS Code, but then again, I specifically do not want to endorse any program.
Edit: Or put another way - if my CS101 course has about 500 participants (which is not unreasonable in Europe), even 1% with whitespace problems will keep you busy and from answering questions that provide real insight and understanding. Because, after all, while learning to distinguish a tab and n spaces is a valuable life skill, it's entirely not my point while teaching how to think when programming.
Edit: Or put another way - if my CS101 course has about 500 participants (which is not unreasonable in Europe), even 1% with whitespace problems will keep you busy and from answering questions that provide real insight and understanding. Because, after all, while learning to distinguish a tab and n spaces is a valuable life skill, it's entirely not my point while teaching how to think when programming.