How much should reviewers care about other things than an article's content? This is a follow-up question to a previous one asking for the potential impact of the typesetting tool (at the review level) on the chances of acceptance for a given paper. 

I'm interested in the general case where reviewers will get a "feeling" of the way the article is presented, be it the writing style, British vs. American English, English from non-native speakers, choice of font, or like in the linked question, typesetting and any other criterion that is not related to the content of the work presented. 

To be clear, I'm not asking about the more obvious or well-documented sources of bias, like the sex, name or geographic location of the authors. This can possibly be addressed by double-blind review.

As an example, I'm used to journal submissions in the form of a PDF with the least possible amount of formatting: plain text, typically not justified on both sides, lines numbered, usually double-spaced, figure captions at the end, figures concatenated at the end by the electronic submission system. Where I publish, typesetting is a journal's thing and as an author I'm happy to delegate that hurdle. 

I once reviewed conference proceedings where the submission was very informal and couldn't help but having a "feeling" from the looks of the submissions. Authors who used LaTeX, which is unusual in my field, didn't look like they had a lot of experience publishing in this field.

I think that ideally this feeling should be silenced and I tried to do so as much as I could. However, reading comments and answers on this other thread made me wonder if that was a sentiment that others shared. My question then boils down to:

Do reviewers have a duty to try to ignore their biases or is the "gut feeling" an important part of the review?

As a final note, I'm not looking for arguments in favor or against the use of LaTeX in general, or in the specific case I mentioned. I find LaTeX to be very well suited for the applications it's intended for and I simply used that example to illustrate something that is not content but could (and apparently does) induce a bias.
I think the gut feeling is helpful during the evaluation process - one can probably not fight it anyway, so I think one should just accept that it is there. However, the gut feeling must not hinder a review based on the content of the paper.

So, what should not happen is, e.g.:


Stop reading after a few pages because you don't like the look, typesetting, language, variable names… (you may, however, stop reading if the style hinders your understanding, which is something completely different). Even if you hate Times New Roman or Arial, be professional and keep reading. 
Keep worrying about issues as above when it comes to write the comments (with the exception of the language, but I am always very careful about comments on language). Comments should mostly address the content of the paper, especially your recommendation should not be influenced by gut feeling. So once you read everything carefully, form an opinion not based on the look of the paper, but on the content (which you have digested at that point and hence, you should be able to evaluate it without taking the look into account).


One exception is figures: If figures are poorly formatted and don't allow to extract the information, this is a serious issue (too small font, pixel graphics with poor resolution, colors that are indistinguishable for common color blindness…). But also here it is more about "can I extract the information" and not about "do I like the look".

Be extra careful with gut feeling if you review something which is borderline for you field. As can be seen in the above comments, the styles of submission vary greatly between fields (extreme example: Some field have all floats, i.e. tables and figures and such, on extra pages at the end of the documents, other field have submission that basically look like a final article, some fields use double spacing, some don't…).