First, of course the U.S. is guilty of much evil, and that has become
rather well known recently. Yes, I think the U.S. should be
boycotted, for the same reason South Africa was boycotted during the
apartheid times: disrespect for basic human rights. And I think China
should be boycotted for the same reason.

Some of the points you mention are valid. It IS ludicrous for the
U.S. to criticise other countries on human-rights issues when they
legislate against certain things adults do in private.

Of course, anyone doing business in a country is expected to abide by
the laws of that country. That's not the question. The question is
whether Google should do business in China at all. The boycott is for
people outside of China to boycott Google outside of China.

A parallel would be a European company operating in the U.S. helping
the local sheriff arrest married couples having anal sex. I think a
boycott by the European (and other) users of that company would be a
good idea.

One can't expect to be given special treatment if one breaks the
laws of a country which one does not like. However, one can and
should protest against such laws, form inside and from outside the
country, and encourage others to do so. If companies would rather
not do business in a country where there are bad laws, that is a
good thing and should be supported.

National laws, of course, are not sacrosanct. Human rights are
absolute and can't be taken out of existence just because some
government doesn't like them. It is perfectly legitimate for
individuals and governments to criticise unjust laws. He who thinks
otherwise, namely that the "internal affairs" of a country should
not be criticised from outside, would presumably not have criticised
Nazi Germany for killing Jews (who, after all, were German citizens).