All of us (all sides of the political spectrum) tend to gravitate to those sources of news and discussion that cause us the least angst. That angst exists because the stakes are so high and the political divisions are so broad.
That said, how are you defining 'mainstream political opinions'? Also, should every effort and every position be determined on the basis of its political costs - or do we follow our principles for those things that are most important to us?
Poll after poll has consistently shown over the years that a majority of Americans support some form of legal abortion but also support restrictions, whether these be parental notification laws or trimester limits.
These opinions are generally not shared on this forum. They are also not shared on the liberal forums where abortion should be offered any time for any reason, a position that is equally out of step with mainstream political opinions.
Winning elections often requires compromise. Holding strongly to principals often means losing. Is it better to compromise your principals and win or hold on to them and lose? In other words, is it better to support the candidate that represents 50% of your views and could win or the candidate who represents 100% of your views but has no chance at beating the candidate who represents 0% of your views?