Will it cause friction?
You don't have to worry about friction between leads/investors when they are hesitant about logging in with their social account.  When a lead logs in, they are logging into a secured network.  They don't have to worry about their information being shared and is protected from the public domain.

Values for you and the leads
The value of having a lead logging in with their social account is to your benefit and the lead.  You are able to monitor your material and track the traffic through your sites.  You will also have the lead's contact information if you want to contact them for any reason.

What if the lead still refuses or don't have any of the three social login accounts?
You have the option to create a short or teaser deck with 4-5 slides, which you can set to public.  Anyone can view the slides but there are huge disadvantages because you will not be able to see who viewed your presentation and don't have their contact information if you ever want to connect with them.