He did no such thing.
He pointed out IF Pope Francis believes that adultery “is what God himself is asking” of couples in “irregular” situations, then there is nothing stopping any other intrinsically evil acts from eventually being justified (quoting1P5.)
“If this is truly what AL affirms, all alarm over AL’s direct affirmations regarding matters of changes of sacramental discipline refer only to the peak of an iceberg, to the weak beginning of an avalanche, or to the first few buildings destroyed by a moral theological atomic bomb that threatens to tear down the whole moral edifice of the Ten Commandments and of Catholic moral teaching,” Seifert wrote. (1P5)
This is true. Plug in any other sin into this logic: racism, defrauding your worker, contributing to climate change, etc. and what have you got? It's not pretty but there it is. If Francis doesn't intend this he can say so. 

Why is this not ok but Fr Martin playing footsie with homosexual acts is?