1) Did they fix the thing where you had to use __self__ practically everywhere? Double underscored variable names also look like crap, especially when they're everywhere. It looks like a really shitty design flaw, having to use __self__ this and __self__ that everywhere. (This situation may have been ameliorated since I last looked at the language.)
2) Not everyone likes significant whitespace. But moreover...
3) If you code for long enough, you'll eventually realize that Ruby, Python, C++, etc. etc. are all fundamentally flawed due to OO making it too easy to write spaghetti-dependency code with mutable state everywhere, which means EVERY OO CODEBASE NO MATTER WHAT eventually becomes an unmanageable bugridden long-test-runtime complexity tarpit.
They should stop calling it "technical debt" and start calling it "object-oriented debt" ;)
So you eventually convert to the Functional Programming™ religion. ;) And that is the real reason not to use Python (or Ruby or Java or C), IMHO. But don't take my word for it, here's John Carmack basically saying that everyone should use functional paradigms (even in OO languages) if at all humanly possible: http://gamasutra.com/view/news/169296/Indepth_Functional_pro...
Both come with tradeoffs, but Rust's borrow checker seems, anecdotally, to be easier for people to understand than the category-theory word salad that litters most strictly-immutable FP language discussions.
A simple example of a single threaded mutability bug is passing an object by reference to a method which then (either intentionally or unintentionally) mutates the object, to the complete ignorance of the caller up in the call stack. The only thing stopping that is literally, programmer skill. No language constructs. At least in all the OO langs I ever worked with.
2) That is a reasonable choice. I like expressing myself once, instead of repeating myself in both whitespace and brackets or whatever, but I get the argument for autoformatting after copy/paste. Of course, lua does this the best, by having neither significant whitespace nor semicolons, and just figuring out where statements end from the grammar.
3) Objects are wholly optional, and can mostly be avoided. the functools and itertools libraries go a long way to bring the functional religion to python.