To you may be it's a simple drawing, but not to hundreds of millions of muslims, may be more, who don't support the killing but don't want to see their beloved prophet being drawn like that.
There's nothing in the Qu'ran prohibiting representations of Muhammad. As a matter of fact, it's commonly done in Shia Islam.
Even ignoring this issue, it's an islamic "law".
Why should non-muslims in a country with a big principle of laicity abide by it? Should french restaurants stop serving lobster because it's forbidden by the Torah? Should coffee shop owners in the Netherlands be arrested because selling cannabis is forbidden in most countries? Should Germany stop raising taxes for the church because in France it stopped over 100 years ago?
Unless you can give a reasonable explanation as to why these things should happen as well, then you have to understand that there is absolutely no grounds for asking them to stop. There is no and shouldn't be a special case for religion. If you start with that, there won't be an end of it.