Market with controversial issues or the idea?

I think the question is which is more important to you, the platform or the individual fundraiser? The site will gain attention through each "poll," however, marketing the site alone may not ensure the success of the different polls. But if it were me doing it, I'd market both. The truth is they are one in the same. If people don't care about what is being challenged on the site, you have no website. Vice versus, they won't care about the website, if you don't have exciting challenges.

So, it would seem that you might have the typical platform quandary -- you need to grow both users/investors, and companies that want to participate in your platform. Which do you grow first?

Growing users/investors is likely the priority. If you have a few companies, then you can grow your base of interested people. If you have enough people who are paying attention--and can cultivate a group that are willing to invest--then you can get more companies.

To raise awareness and grow the user base, I would focus on the controversial issues, which will be more likely to pique interest and to get people watching and engaging. Perhaps find some way for people to participate without investing, and a reason why people should share.

You can use PR to tie both the controversy and the model together, and use marketing and social media to promote the controversy.

I would go with promoting the matchups for two reasons,

1) People identify with causes not formats.
2) If the matchups are well paired the natural competition should drive contributions

Personally I am intrigued by your concept and will be following how you develop.

If you’re like a lot of other technology managers and event organizers, you’re probably grappling with issues related to how best to promote your organization’s events online. While you undoubtedly have dozens of very specific requirements in mind, your ideal website calendar solution most likely includes these four high-level characteristics.

Convenient. Are you tired of the labor-intensive website calendars you currently maintain? Frustrated at watching highly paid IT professionals inputting and updating events? The ideal solution will definitely be convenient to implement and easy to maintain.
Flexible. The last thing you want to worry about is remembering to update the same information in more than one location. What you need is a website calendar solution that allows you to call your event data source from different pages on your site so you can present the same information in different ways to different audiences.
Customizable. When you publish event information on your website, you don’t want it to look like it comes from some third party application. The ideal solution gives you control over the content and appearance of your events so that your online calendars reflect your organization’s brand.
Engaging. At the end of the day, you want a website calendar solution to increase awareness of and attendance at your events. That’s a tough guarantee for any solution to give. It seems perfectly reasonable, however, to expect the ideal solution to engage site visitors by providing interactive calendars that make finding and remembering to attend events as easy as possible.
Does this ideals list sound a little too ideal to be true?

On the contrary. The ideal can be real today using a web-hosted online calendar solution that supports a spud-based delivery model.

Provide Interactive Calendars And Events
Because spuds are interactive, site visitors are more likely to find events they care about and remember to attend them. The What To Do page on the Pocono Record website demonstrates the power of interactive spuds.

Pocono Record What To Do page spuds

Click Submit Event (1) to submit events for inclusion in the Calendar spud (4) (editors review all submissions).
Choose values from one or both filters in the Filter (2) spud to create a filtered list of Calendar (4) events.
Choose a view in the View Chooser (3) spud to change the way the events in the Calendar (4) display.
Select one or more events (5) in the Calendar (4) spud and then choose an event action (6) to add events to your personal calendar, set reminders, and more.
Click one of the subscribe options (7) to receive ongoing notification of upcoming events through an iCal, RSS, or Atom feed.
Click a date in the Date Finder (8) spud to display events in the Calendar (4) spud that occur on that date. Hover over a date to display a list of that date’s events.
Type one or more keywords in the Search (9) spud and click Go to start a full text search of all of the events in the Calendar (4) spud.
Conclusion
Web Widgets are dynamic, customizable, interactive programs you can add to any web page that operate independently from the rest of the page. As a specific type of event-related Web Widget, spuds offer you a convenient, flexible way to publish customizable calendars and other event information on your website. Because spuds are interactive, site visitors can easily find events they’re interested in, add events to their own personal calendars, and take other actions.

For further queries you can consult me.

I worked as a corporate & startup marketer for 12 years before starting my own marketing education and services company.

Launching an outlandish challenge would be great for PR and exposure. In your example, NRA vs Students for Gun Control becomes a human interest story because the results serve as a litmus test of which side of the fence people are more likely to financially support.

The only hurdle would be finding a source of momentum to keep the challenge going. GoFundMe works well because there is an individual invested in the campaign being successful. In the way you've descried your challenge it seems it would be run by your platform without participation from either side to support it. I would look into getting the opposing sides involved to spread the word. A company that does a good job of leveraging momentum in the charitable giving space is Omaze.

Happy to have a call if you have any additional questions!