Why did Augustine attempt to stop Christians from walking barefoot? In The Confessions, Augustine relates the story of an ascetic named Alypius who "tamed his body" to such an extent that "he went barefoot on the icy soil of Italy" (IX.vi).  Henry Chadwick notes:


  Much ancient evidence records the axiom that for cultic acts bare feet are necessary; Augustine himself found it impossible to stop the practice when he became a bishop.  Monks in ancient Egypt removed their shoes for communion.  In Syria it was customary for candidates for baptism, in the West for Regation processions.


Apparently, then, some Christians walked barefoot only for short times associated with communion or baptism, while others went without shoes for long periods, even outdoors during the winter.  Chadwick's note makes it sound as though Augustine objected to the practice generally, not just to the extreme forms, but this isn't clear. So:

Did Augustine attempt to stop Christians from removing their shoes for all types of worship and ceremonies (if so, why?)?  Or was he only concerned about the more dangerous types like that done by Alypius?  Where in his writings does he address this topic?
I think that Henry Chadwick is conflating Manichaeism with Christian asceticism, toward which he appears to have a bias.  He clearly indicates in another work - Priscillian of Avila: The Occult and Charismatic in the Early Church - that he had Manichaeism in mind when he interpreted the passage, but also considered certain non-canonical Christian ritual ascetical practices.  Georgetown Professor James O'Donnell observes (here), however, that although the latter troubled Augustine, he did not think it merited a severe rebuke, as he attests in his Letter No. 55:


  I cannot, however, sanction with my approbation those ceremonies which
  are departures from the custom of the Church, and are instituted on
  the pretext of being symbolic of some holy mystery; although, for the
  sake of avoiding offense to the piety of some and the pugnacity of
  others, I do not venture to condemn severely many things of this kind.
  But this I deplore, and have too much occasion to do so, that
  comparatively little attention is paid to many of the most wholesome
  rites which Scripture has enjoined; and that so many false notions
  everywhere prevail, that more severe rebuke would be administered to a
  man who should touch the ground with his feet bare during the octaves
  (before his baptism), than to one who drowned his intellect in
  drunkenness. My opinion therefore is, that wherever it is possible,
  all those things should be abolished without hesitation, which neither
  have warrant in Holy Scripture, nor are found to have been appointed
  by councils of bishops, nor are confirmed by the practice of the
  universal Church, but are so infinitely various, according to the
  different customs of different places, that it is with difficulty, if
  at all, that the reasons which guided men in appointing them can be
  discovered (XIX.35)


I would submit, however, that although Augustine may have objected (mildly) to 
non-canonical ritual Christian ascetic practices, he did not object to Christian asceticism in general.  This is evidenced in how he refers to the Egyptian monk, Antony (Anthony the Great), one of the strictest ascetics of his time:


  A conversation ensued on his [Pontitianus, a Christian] speaking of
  Antony, the Egyptian monk, whose name was in high repute among Thy
  servants, though up to that time not familiar to us. When he came to
  know this, he lingered on that topic, imparting to us a knowledge of
  this man so eminent, and marvelling at our ignorance. But we were
  amazed, hearing Thy wonderful works most fully manifested in times so
  recent, and almost in our own, wrought in the true faith and the
  Catholic Church. We all wondered — we, that they were so great, and he,
  that we had never heard of them.
  
  Confessions, Book VIII, XII.29


I think further evidence of a bias against Christian asceticism comes out in the way Chadwick chose to translate the Latin, fortissimo dominatori corporis, usque ad Italicum solum glaciale nudo pede obterendum insolito ausu (IX.VI.14).  Chadwick's translation reads, as you cite:


  ... and tamed his body to a tough discipline of extraordinary
  boldness: he went barefoot on the icy soil of Italy.


By comparison, the translation in the Nicene and Post-Nicene Fathers edition of Confessions reads:


  ... being so brave a tamer of the body, as with unusual fortitude to
  tread the frozen soil of Italy with his naked feet.


Other translations:


  ... a most valiant tamer of the body, so as, with unwonted venture, to
  wear the frozen ground of Italy with his bare feet [Pusey].
  
  ... and was so brave a tamer of his body that he would walk the frozen
  Italian soil with his naked feet, which called for unusual fortitude [Outler]


Augustine attempted during his life to end not only certain ascetical practices associated with Manichaesm, but indeed the cult itself (to which he at one time belonged), as evidenced by the large corpus of work he wrote against it (e.g. On the Morals of the Manichaeans, Concerning Two Souls, Disputation against Fortunatus, Against the Epistle of Manichaeus Called Fundamental).  This is not to say, however, that he condemned similar ascetical practices undertaken by Christians for entirely different purposes.  

I would submit that the short passage cited, when translated appropriately, shows Augustine's support, rather than disdain, for Christian asceticism.

This apparent bias against Christian asceticism reflected in Chadwick's comment seems not to be unique.  The editors of Augustine's Anti-Manichaean Writings in the Nicene and Post-Nicene Fathers series make the following statement, without any further elucidation or support, in their introduction:


  Many Christians were in a position to be attracted strongly by the
  Manichæan theory and practice. The later asceticism as it appeared in
  the hermit life of the fourth and following centuries was essentially
  pagan and had much in common with the Manichæan.