I think it totally depends on what the volunteer experience is. I would suggest that only occasionally would an employer see it as negative, however, here are some scenarios where you may consider leaving it off - such as:
-You volunteer at an organization that creates political or societal polarization - i.e. a very conservative controversial church, or an organization like the ACLU that people typically have strong opinions about (can be positive or negative, but nearly always strong).
-Your volunteer activities suggest that you are more interested in volunteering for a specific cause than working for a paycheck. Employers are looking for stable, hard-working employees that will benefit their organization, so don't do anything that suggests you don't fit into that category.
-You volunteer for any type of political organization - politics are so polarizing right now that your experience may help you with 50% of potential employers and hurt you with another 50%. Given that most positions are hired with input from multiple people, a particular political persuasion runs a lower chance of being seen as positive to everyone on a committee than a single individual.
Employers do want well-rounded individuals, but their primary concern will be their devotion and skillset for the job they are hiring for. If all else is equal, the extracurricular activities will typically be beneficial, as long as they are not super-controversial.
And as an employer, we are not looking for a reason to weed out a resume. The last couple of jobs my company posted had 100-300 applicants, so we're looking for the candidates who have the most applicable experience who fit our vision of the type of employee we want to hire.
Honestly, we don't have time to interview 100-300 people, so we're looking for the top 5 to 10 people who fit the "mold" we're looking for.
All employers will have some pre-conceived idea about the type of individual and certain traits or experiences that will best suit the job, so trying to broadly appeal to the greatest number of employers gives you the greatest chance of getting an interview.
Probably the most important part about a resume is having it be clear, concise, and communicative of your strengths and experience in a way that can quickly communicate what you can do to a potential employer.
I probably give the average resume 10 seconds or less before it gets boxed into a category. Not because I don't want to read all 300 resumes, but because I simply don't have time to. So make sure a quick skim of your resume makes an employer want to re-read it more thoroughly. Things like clear formatting and ensuring that spelling and punctuation are accurate are very important.
Last tip - write a personal (and unique) cover letter for each job you apply to. Having great communication skills is a plus to every employer. And if you can communicate briefly and effectively how you could benefit the company by being hired for the position you're applying for, that's like gold to an employer.
That's my 2 cents, for what it's worth...