Let me state upfront that I believe suicide ganking and highsec wardecs are an important part of EVE Online. The element of danger, even in "safe" highsec space, gives weight and meaning to resources.
I started playing 2.5 months ago, and stuck to high sec until moving to low sec recently. Even during my time in highsec, the exhilaration of hauling 200+ million ISK through ganker systems, and evading gate camps during a war dec was what drove me to upgrade from Alpha to Omega. IMHO "even highsec is not safe" is a vital aspect of EVE that should never be changed. That being said, I believe that high sec wardecs
might have an impact on player retention, based on personal experience and other threads on this forum.
I have an alt in an alliance that gets wardecced semi-frequently by alliances that are larger, have much higher skillpoints and much more expensive ships. So there is no easy way to fight back. And when we try to fight back, the wardec often gets renewed as PvP action is what they are looking for. That being said, I'm a seasoned gamer and so had no problem staying alive through the war. Likewise for many of my alliance mates, especially those in my corp, which often operates in low sec.
The people who suffers the most are the new players in our alliance, especially those in non-PvP corps (mining, industry etc). I have seen some these corps fall apart, and new players leave because wardecs are essentially turning high sec into low/null sec. This appears to be a common trend in threads complaining about high sec wardecs.
I believe that being in a corp, socializing and getting guidance from other players plays a big factor in getting players to stay/subscribe. These non-PvP corps in my alliance are contributing a lot by putting in the time and effort to recruit and guide new players. It feels like a huge missed opportunity when they fall apart due to wardecs.
CCP's official stance is to stay in NPC corps to avoid war decs:
https://support.eveonline.com/hc/en-us/articles/204873262-Known-Declared-Exploits. Unfortunately, staying in an NPC corp means that new players will not be able to take part in the social aspects of EVE. This does not feel like a good way to retain players. It feels like there is a step missing between NPC corps and wardec vulnerable player corps.
I'll leave it to the professional game developers at CCP to figure out if this is an issue and how to fix it. But off the top of my head (not fully thought out at all), a possible way to do this might be to allow players that are less than X months old or have less than X skillpoints to join a corp as a "probationary" member that is not a valid war target but has severely restricted privileges to prevent abuse. Or even allow a corp type, that are highly restricted, between NPC and full blown player corps. These will give new players access to social tools without needing to take part in the wardec system, and at the same time not allow them to enjoy the benefits of a corp without risk.