From the Lubavitcher Rebbe:
Greeting and Blessing;
I am in receipt of your letter in which you ask my opinion "as to whether it is a weakness or impropriety" to avoid the purchase of goods made in Germany. You add that you ask this question as a Jew, in light of Jewish law and custom.
Surely this is more a matter of feeling rather than a question of Jewish law and custom. Consequently, as in all matters of sentiment, it is difficult to express an opinion that would have universal application.
At any rate it certainly cannot be categorized as a "weakness". On the contrary, a decision of this kind bespeaks strength of will, all the more so since it entails some inconvenience.
Nor can it be considered an "impropriety", since it is based on a principle which may be considered to come under the category of "Remember what Amalek did unto you". For, as is well known, the inhuman atrocities, etc., against our defenseless and innocent brethren were not perpetrated by a small group, but were carried out with the knowledge, consent and even cooperation of the vast majority of the German nation. Moreover, I do not think than anyone seriously believes that the Germany of today is entirely different from the Germany of two decades ago.
While on this subject a point must be made which, unfortunately, is often overlooked. It is that the so-called "Final Solution", which Hitler wished to bring about, can take various forms. It can take the form of an overt attempt at physical extermination, or it can be an insidious process which is no less destructive and perhaps even more so, namely, through assimilation and intermarriage, a process which began in Germany long before Hitler, when Jews tried to hide their Jewish identity and conduct their daily life like their German neighbors and associates, etc. This process, most unfortunately, is very much in evidence all around us. Whatever explanation may be given, the effect is the same. Hitler, too, had a "philosophy" that "justified" his actions.
It is too painful of a subject to dwell on here, but the conclusion is obvious. Each and every one of us who is aware of the situation must do everything possible to counteract the tide of assimilation by positive and dedicated action, to strengthen the eternal Jewish values and Torah-true institutions in his community and environment.
With blessing,