Whether or not it's true that the data throttling is unintentional, by being publicly hostile to the EFF, he's losing customer goodwill that's one of the biggest things T-Mobile has going for them.
... seems to be happening, at least today on twitter, and I think its worth worrying about. Bloggers and journalists seem to have a better grasp of the issues, so maybe it'll backfire against Legere.
Probably not. Best case, EFF comes out unscathed. Worst case is they have less goodwill then before.
There is no way this works out poorly for T-Mobile, only the EFF.