There is not supporting IE, and there is blocking IE. You are blocking IE - I know because I changed my user agent on my firefox browser and you blocked me, and that is not cool! You don't even offer an option to let me try anyway! Use feature detection if you must, ignore IE completely in testing if you wish, but do not actively block it or you are just as bad as those who only support IE.
Completely disagree. There are two very major problems with this idea: 1. Your reputation suffers when users encounter issues while using the browser that you don't support. 2. The support cost of "letting users try anyway" is non-zero, and probably significant.
However, they sometimes offer a "try anyway"-link and sometimes not. The times that I can not easily "try anyway" makes me dislike Google much more than the times that I "try anyway" and it ends up broken in funky ways.
Bottom line; Yes, your reputation suffers when users encounter issues. Your reputation also suffers when users encounter the big blocking issue of not being welcome at all.