People often interpret the use of capitals online as if the author is SHOUTING or YELLING at them. Using all caps may be considered offensive and aggressive to many readers.
Instead of using capital letters to make a headline stand out, try other formatting to achieve the same effect. Making the word or phrase bolded, a different color and/or font size, or in a coordinating font type can make text more noticeable. Additionally, extra spacing around a headline can make it stand out from a regular paragraph.
But remember to keep the effects to a minimum - when you try to make everything stand out, nothing does.
