So basically the problem is that there are people who know that creationists frequently spread misinformation in support of their religious views. Of course anti-scentific religious zealots are going to have problems getting their views into scientiifc publications - but not out of any policy or prejudice on the part of the publishers.
Scientific American didn't ban Rorrest Mims or refuse to ever publish anything he wrote. They just didn't hire hme to write a column because they knew he couldn't be trusted on some subjects.
The editor of Scicne knows that creationist letters are usually not worthy of publication in that journal. Is that a surprise to anyone ?
ANd the last tiem I encountered Humphreys claim I checked the letter policy of Science and the phrase about representing all opinions was NOT present. (Of course if it were, a letter-writing campaign by any group could get any view into the letters column so there seems to be good reason not to make it an overriding rule as Humphreys claims).n