I strongly favor correct grammar in all settings where we should expect it. I even go a step further that correcting missed and misplaced capitalization are not minor edits. I favor that we correct these items now.
Grammar is the first indicator of professionalism, and professionalism is a goal for all SE sites. We strive to make the internet a better place and create a space with a high level of signal to noise. To me, and I think to many others, incorrect grammar and lazy capitalization looks like noise. In the least, our noise should still look like signal.
This leaves us with this question: where should correct grammar be used. For me, that line is everywhere except where programming requires normalized text. For example, tag names are normalized to lowercase because they serve an organizational/programming function. As an amateur programmer and web developer, I actually expect that*. In the tag excerpts, which does not exist for any programming reason, I expect correct grammar. It exists solely to define tags for the end user to understand.
For some smh feelings for the programmers, tag synonym search is case-sensitive**, which breaks the whole reasoning for normalizing tag names in the first place.
*Oddly, we can perform all normalization behind the scenes, on the fly, but knowing that tags are a programming artefact that happily double-serve as a quasi-meaningful metric leaves most of us with the expectation that it should look like a programming thing, even to the end-users. This might make for an interesting study on User Experience SE. Feel free to follow up there.
**SE staff are looking into the bug already, so don't post on meta.