However I find myself being disagreed with quite often, mostly for not advocating or cheering violence, "by any means possible" change, or revolutionary tactics. It would seem that I'm not viewed as authentically holding my view unless I advocate extreme, violent, or radical action to accomplish it.
Those seem like two different things to me.
Edit: TO COMMUNISTS, ANARCHISTS, OR ANYONE ELSE CALLING FOR THE OVERTHROW OF SOCIETY
THIS OBVIOUSLY ISN'T MEANT FOR YOU.
Yes and no. The answer isn't straightforward, so let's unpack it. Primarily, the qualifier "validly" needs investigation.
What is "validity" when it comes to political positions? Is validity a measure of correctness? Is validity a measure of intention?
If validity is a measure of correctness, then yes, you must be revolutionary if you are a Marxist or Anarchist, the two dominant trains of Leftist thought. Fringe positions like Social Reformists exist, though they have never been successful in achieving anything that can be considered long term leftward progress.
If validity is a measure of intention, then no. Not every progressive-minded person has done thorough research into leftist history, theory, and practice. Progressives can have an idea of what end result they want, without yet putting in the work to understand how to get there.
In the body of your text, there are loaded statements. To be Revolutionary isn't to "celebrate violence," or believe "by any means necessary." Revolutionaries do not oppose Reformism, but believe it a lost cause. For a US-centric example, Reformism would be possible if PSL, the Party for Socialism and Liberation, could win elections consistently, but they cannot because of the two-party duopoly, created by Capitalist investment.
By and large, whether someone is a Revolutionary or Reformist doesn't come down to purity, but knowledge and positions.
I should have just stuck with Democrat, and gotten rid of the whole idea of leftist and liberal.
You can, if you want. If you generally agree with the DNC, labeling yourself a Democrat is a useful label to quickly get your views across. You wouldn't be a Leftist, since the goals and views of the DNC are a maintaining of the Capitalist status quo, but you would be a Liberal, if you want a non-party label to use instead.
I do think familiarizing yourself with Leftist theory would help you make sense of where Leftists are coming from.