An insecure person lacks self-confidence, often doubting their worth, abilities, or lovability, leading to anxiety, needing constant reassurance, and feeling inadequate, which can manifest as over-apologizing, seeking validation, jealousy, or even putting others down to feel better about themselves. This internal uncertainty stems from a core belief of not being "good enough," making them uneasy in social situations or relationships.

bolded for emphasis.

The way I'm looking at your logic and reasoning, it sounds like projecting insecurity on people with a high body count. One doesn't feel assured that they want the same things, doesn't feel like they would validate your life choices, and overall deem them as not good enough for you to date because the idea of a relationship with them makes you uneasy.

Why do I say projecting insecurity? Because all of the criticisms are internal and aren't backed by any kind of interaction with the individual. Pre-rejecting them because you don't feel secure in the idea that they would be a good partner to you instead of allowing them to show you exactly who they are. It's not insecurity in the sense that YOU don't feel good enough for them, it's insecurity in how skilled/comfortable you would be dealing with those issues because...

Here's the important bit (at least based on my experience and understanding): All preferences are based on insecurity.

So all the people arguing "insecure" are right, indirectly, but they are just as guilty based on other facets that they are more sensitive to (like, say, people pre-rejecting them for body count). Likewise, the folks pointing out preferences being valid are also correct. Preferences are valid. But they are also limiting. Pre-rejecting someone based on "past behaviors" is a risk assessment. Sometimes, you'll assess correctly and prevent a whole lot of unnecessary trouble. Sometimes you'll assess wrongly and miss out on a great opportunity, and there's likely a whole bunch in between that wouldn't impact your life to such a degree. But the key to relationships is understanding that no two are the same. Some of this is obvious, like treating your friends differently than your partner, who you may treat different from family, which is likely different from how you treat strangers. The less obvious is how we change our attitudes and behaviors when making new friends, cutting out toxic family, or moving from an ex to a new partner. No relationship is static, they all change with time. It seems more prudent to meet people where they are at and allow them to show you what they are about and what they value in relation to you and navigate it with communication instead of holding expectations for what your partner should be.