Genealogy researchers have typically shied away from unsightly commercialism. We need to accept a new form of commercialism. I could easily scroll past an ad for Welch's Grape Jelly to get the scoop on an ancestor's Revolutionary War record. The only real interference would be if I actually got some of the grape jelly from my peanut butter sandwich on my keyboard. The real fact is it costs money to run a web site.
Someone has to pay for it.
If genealogists aren't willing to pay subscription fees to offset costs, then advertising is the alternative. More Source Documents Online references to ancestors are not considered first-hand or primary sources of information. It is most certainly at least one step removed from the original document. Even if someone painstakingly typed in all the information from an old will sitting on the desk beside his keyboard, you must admit there will understandably be transcription errors. It is humanly impossible to decipher every single word of an ancient document without error.