Why are any judges allowed to contribute to political campaigns? Isn't this blatent partisanship?

First amendment.
That's why recusal happens -- judges still have the rights of citizens, which can led to conflicts of interest,

Scott, Judges (and judicial candidates) cannot make political contributions to political candidates. Those contributions are barred by Canon 5 of the Minnesota Code of Judicial Conduct. The political contributions in question (Dietzen, Gildea, and Meyer) were all made before these persons were appointed to the bench (and, therefore, before their actions were governed by the Code).

This issue has been hashed and rehashed, but IMHO the only donations that are close calls are Justice Dietzen's two contributions in years leading up to Coleman's 2008 re-election bid (and, obviously, before he was appointed to the Minnesota Supreme Court). The other donations were to different candidates, and I'll bet you dollars to donuts that every single judge on that court has made political contributions to political candidates at some point in their lives.

Justice Dietzen was obviously aware of the contributions before he participated in earlier decisions in this case, and just as obviously has made the decision that the circumstances do not warrant disqualification. (I skimmed the Code and didn't see anything demanding disqualification; presumably he spent a lot more time considering the issue....) At the very least, it creates a bright line so we're not in a tit-for-tat situation where Republicans push for Justice Meyer to recuse herself.

We have a fairly non-partisan court, but obviously most of these judges have political (if not partisan) backgrounds. Nonetheless, we expect them to leave that behind when they are appointed to the bench. Say what you will about the relative merits of the state and federal judiciaries, but I am much more confident in the Minnesota Supreme Court to render an unbiased non-political decision than I would be if/when Norm appeals to the U.S. Supreme Court.