Are practices of such kind discouraged?
That's a tough one. As @Zanna said your question wasn't bad. It's just possible that some users saw it as not being a great fit for this site. As @Zanna mentioned, downvotes on questions are important to "help along the Roomba."
But for reasonable questions like yours, that are closed as off-topic, I personally would never downvote if the score was already -2 or lower. I do see this as "piling on", and discouraging to the OP (you, in this case, of course).
That said, sometimes when there's a -2 score, one or two more users will come along and do a (presumably) "sympathy upvote" that can return the score to Roomba-ineligible status.
However, it seems to me that the "Stack Exchange" auto-ban algorithms also likely take into account the number of downvotes on questions. You certainly won't be temp-banned for a single "bad question", but having other downvoted questions combined with this "highly downvoted" question could trigger a ban faster than having just several "slightly downvoted" questions. This is all complete theory on my part, as we don't know how the actual algorithms are implemented (intentionally so).
For this reason, I would only "pile-on" on a really bad question where corrective behavior for the user may be warranted if they repeat the behavior consistently.
In addition to the reasons that @Zanna mentions about people seeing your question as a "feature request" to Canonical, there's also the possibility that some users saw a lot of bold text in your question and voted because they perceive that as shouting, similar to ALL CAPS.
I personally do not like a lot of bold text in a post. It seems unnecessary to me, and jarring, and it does look a lot like Internet shouting, even though I know you didn't mean it that way. I didn't see or vote on your question prior to seeing this Meta question, but if I saw a question that I felt was off-topic, and it had excessive bold, that would usually garner a downvote from me.
I would propose a light emphasis is typically more appropriate for posts, and I've made that edit your post.
As for whether it is "Opinion-based", I respect @Zanna's views a lot, but I would still consider this one as being (just slightly) "too subjective" to fit here at first glance. I don't arrive at this view on the basis that "Only Canonical can answer it." However, it seems to me that answers to it must inherently discuss the advantages and disadvantages of the various methods, and it feels like answers would far too easily devolve into the type of "Discussion Answers" that we try to avoid here.
But while I wouldn't personally vote-to-reopen, I definitely wouldn't "pile on" downvotes here either ;-).