Number one, they got bogged in the mud because their initial plan envisioned advancing 500 kilometers into USSR, after which it will collapse and war would be effectively over. This did not in fact happen.
Germans recognized logistical impossibility of Barbarossa, but decided to ignore it, hoping it will all end well.
It is not due to fear of being accused a defeatist that they didn't pack for winter, but they realized if it took them until winter to complete the campaign than it would have failed regardless of any other consideration. Most German generals realized operation failed in July, when Soviet Union failed to cease to exist. Reality is that, no matter what, Germans do not have nor will ever have, the capacity to supply their troops beyond first 500 kilometers until they repair railways leading to the front. So unless you have a solution for this (and many have been suggested and tried, both by contemporary German generals, and by armchair generals with hindsight) Barbarossa will not work.