I'll say this: when I first read the question, it seemed inane, and trivial. After all, our FAQ reads:
The English Language and Usage Stack Exchange is for linguists, etymologists, and (serious) English language enthusiasts.
You should only ask practical, answerable questions based on actual problems that you face. Chatty, open-ended questions diminish the usefulness of our site..
At first glance, I can see why your question - about how to spell blah blah blah - would be considered trivial, and hardly the right material for this target audience. It seems chatty, irrelevant, and easily answerable. Blah blah blah sounds like yada yada yada; it comes across as something between baby talk and “What-evah!”
Upon doing some research, though, the question turned out to be more interesting than it initially appeared on the surface. I found 5,000,000 or so Google hits for blah blah blah-with-an-h, but 1,000,000 or so, for bla bla bla-sans-an-h. I found blah in the dictionary, but I found a few instances of bla bla bla cited at a dictionary website as well.
If your question is simple and can probably be easily answered by looking it up, then you may find common online internet resources to be of some help.
You mentioned that "I had checked it out on some online English dictionary and Google search but I wasn't able to clear it out," but you never went on to explain what you found, or why the matter was still unclear.
Given how juvenile the question appears on the surface, but how not-so-straightforward it appears after doing some preliminary research, it's not hard to understand why your question accumulated so many upvotes and downvotes (11 to 10 at this juncture).
I didn't vote either way; I'm a bit torn on the matter. On one hand, the question seems chatty and pointless – an idle argument between you and a friend; on the other, it has some interesting aspects that many have already discussed. On one hand, you took the time to mention that you had checked Google and the dictionary; on the other, you never bothered to tell us what you found there.
As to whether or not the ensuing votes were unfriendly, I'll offer this advice: when asking a question that could easily be construed as inane or irrelevant at first glance, you might try offering more concrete evidence as to why this is a question that would really interest us. Had you gone on to elaborate on what you found, for example, and let us see for ourselves how this problem might be interesting – by including, for example:
I found one poet who said that bla bla was an original spelling: I write 'Bla' the french way...was first said in 1763 in a court room when the accusded said to the Judge ' bla bla bla' then he got his head cut off....200 hundred years later in USA they say now ' blah Blah'
Even though the 5,000,000 Google hits seem to support my friend, I found plenty of other hits that suggest there might be alternate spellings, such as...
then that might have appealed to our collective curiosity, and warded off some downvotes. (There's no way to tell for sure, but I still think the question could have been presented a little bit better.)
I hope that you decide to eventually test my theory by presenting an equally interesting – yet slightly better framed – question sometime in the future.