Yes. If I didn't consider them facts then they wouldn't be my opinions, or maybe they'd be my tentative opinions or things that I consider "probably" true, in which case my statement would reflect that, such as by use of the word "probably."

it's not like there's any easy/universal way to distinguish between what a fact is and what an opinion is. They're both things the person considers to be true, and we don't have access to some outside, absolute truth to compare our beliefs to. You could take it to a logical extreme and say that all purported facts are actually opinions, because we could always be wrong; we're fallible, so ultimately so all our purported "facts" are surmisions.

Of course, you can draw distinctions like "facts are based on evidence/proof" or you could say that opinions about more abstract things, like who would make the best president, are inherently subjective and hence can't be factual. But the problem is that there's no clear line between what things are proven or provable and what things aren't, or between what things are concrete vs. what things are abstract, or whatever. How stringent are your criteria for proof? It's all on a scale, the only things that can be absolutely proven are conjectures in math and formal logic. Where you draw the line is arbitrary, and how measuring where something falls with respect to that line is uncertain.

You could say that "who would make the best next president" has to be opinion because there's no way to formalize it as a statement about things that can be objectively observed, but you wouldn't expect someone to add that something is "merely their opinion" if they made a statement like, "it's better when people have clean drinking water available," even though there's no way to objectively quantify that. Some such opinions, such "Bernie Sanders should be the next president", can be just as functional and effective, but the fact may only be obvious to people who are more psychologically healthy, intelligent or generally aware than others.

So even though people tend to think that we're obligated to, or that it's only intelligent to, regard these things as mere opinion or to qualify any such statement with the fact that it's "just my opinion," on the bases that everybody has their own opinion and there's no way to objectively measure their truths, I think that that view is short-sighted or misled; it shouldn't be applied to all cases.

So there's really nothing wrong with stating opinion as if it's fact, in my opinion.