Why do people say blitz chess can be bad for your chess? I keep hearing blitz chess is bad for you but the I've only been offered two explanations for why that is. The first reason I've been told is that it ruins your ability to focus since you it forces you to play fast so I suppose they say it makes you less patient as well. The second was that blitz is not a very efficient way of improving chess since you can't put as much thought into it in general. But surely that isn't the only reason people say not to play blitz right? After playing blitz I still maintain my ability to focus and as long as it doesn't make me play chess worse I should be fine with reason 2. I really want to understand what this whole deal is about since with my personality if I play blitz or play around with chess in an absent-minded or quick manner I get paranoid and start thinking "Oh no, am I making myself worse at chess or something like that?".
I am answering only as an expert player, so who am I to answer this, but I think that "blitz ruins your chess" was a very popular view some time ago rather than nowadays... Anyway, given the very limited time at your, and your adversary, disposal, in blitz chess a player is not generally searching for the best move(s) but the one that gives you most chances. This may encourage, in the long run, a player to "stay away" from very deep considerations, tactical or strategical, and this is ultimately not good for improving chess strength. When you face strong players with plenty of time at their disposal you have to find the best moves, because they haven't 30 seconds on the clock or so, unless they are in zeitnot, to answer you.