Fair point, Ardee. Both Kiel and Wilhelmshaven were very heavily bombed by the RAF during the war, and most of the cities and their industrial areas were, eventually, either destroyed or damaged. However, while this bombing started as early as 1940, the bulk of the damage would have postdated the 1942 date of the St Nazaire raid and I believe that Kiel, in particular, was never fully knocked out. That having been said, naval repair facilities at the German ports were increasingly limited from about mid-1943. This may have influenced the increasingly cramped deployment of German surface warships (including the Tirpitz) late in the war. Also, there is little doubt that the entry of the Tirpitz into the war did provide particular impetus for the St Nazaire raid in 1942 - though, at that stage, Wilhelmshaven and Kiel were still reasonably close to full operation - something attested not least by the fact that the pre-commissioning Tirpitz had slid down the launching ramp at Wilhelmshaven only a few months before.
There is another factor to be borne in mind when considering the St Nazaire raid - Churchill’s obsession with maintaining some level of Allied land action in Europe through Commando-type raids. This produced several highly successful, not very costly operations from 1940 on, but also produced the very successful, but very costly St Nazaire raid in 1942 and, of course, the disastrous (if educational) Dieppe raid. This is not to say that the St Nazaire raid was not justified by the presence of Tirpitz and other substantial German warships in the Atlantic. It does, however, leave us with the question of whether the Allies had the alternative (less elaborate and less risky) of eliminating the threat from the St Nazaire dry dock and related facilities by means of aerial bombardment. Certainly, this option would have existed in 1944. However, “bunker busting” bombing technology was very much less developed in 1942. Another question - how willing would the Germans have been to expose such a major naval asset as Tirpitz - having suffered damage - to a crippled cruise to the northern part of the Bay of Biscay, and to a facility seriously exposed to Allied air, surface and other forms of attack and sabotage, if even a damaged Kiel was an alternative, even in 1942 ? These are not quite the standard “road not taken”-type "what-if"s, but I am getting close, so I had better stop.
By the way - as mentioned above, Tirpitz was built at Wilhelmshaven and trialled and complete-fitted out at Kiel. Her sister-ship Bismarck was built at the Blohm und Voss shipyard at Hamburg - another (if slightly more limited) string to Germany’s military ship-repairing bow. Best regards, JR.