Stratasys' (NASDAQ:SSYS) strong second-quarter earnings results are now in the rear-view mirror. So, this seems an opportune time to examine the leading 3-D printing company as a potential investment.

In this piece, we look at three reasons why Stratasys' stock price could fall. To be clear -- this is not a declaration that any of these things will happen or that the stock price will fall. We're just examining the merits of a bear argument thesis, as all investors should occasionally do with their stock holdings.

Source: Stratasys

1. The market could turn against 3-D printing stocks due to macroeconomic or industry-specific concerns
The market could turn against highly valued growth stocks in general due to macroeconomic factors, such as geopolitical tensions or economic concerns. These factors often cause investors to flee to less volatile dividend-paying stocks. Alternatively, any less than stellar news about 3-D printing technology in general would almost surely cause a sell-off in Stratasys and its 3-D printing comrades. Such news could ignite concern that the technology's growth prospects might not be as rosy as predicted and/or that growth might not come as fast as projected.

How likely are either of these events? The macroeconomic shock scenario is fairly likely over the short and intermediate terms and very likely over the long term. There's always going to be something not so good going on in this big world. However, this isn't a factor that long-term investors should concern themselves much with, as the market has generally bounced back within a relatively short time from most such traumas.

While it is possible that some negative news could come out of the blue about 3-D printing technology, it doesn't seem likely. This tech has been making great strides lately, and big companies such as General Electric are pouring money into research and development, which should help it make further advances. While this bad news scenario seems unlikely, it would be one to take seriously.

2. Prime competitor 3D Systems could have a huge success
Let's say that 3D Systems hits a home run with either its metal 3-D printer offerings and/or its high-speed, continuous 3-D printing platform that it's developing for Project Ara with Google.

Any huge success by its prime competitor could have two possible implications. If the market believes a similar success is replicable by Stratasys, than Stratasys' stock price could ride the coattails of any upward movement in 3D Systems' stock price. If, however, the market believes that 3D Systems' success means that it has taken a giant technological leap ahead of Stratasys, and Stratasys isn't likely to catch up anytime soon, Stratasys' share price could fall.

How likely is the latter scenario? I'd not lose any sleep over it if I were a Stratasys' investor -- at least not yet. Stratasys is performing very well without selling printers that can print in metals. It churned out organic revenue growth of 33% and 35% in the first and second quarters, respectively, and its total revenue soared 54% and 67%, respectively. While adjusted earnings were under pressure in the first quarter due to the company's growth strategy, adjusted EPS rose 22% in the second quarter. It's also important to remember that while Stratasys still doesn't sell metal printers, its service segment now has metals capabilities, thanks to its recent acquisitions of Solid Concepts and Harvest Technologies.

Granted, the high-speed platform that 3D Systems is developing could prove very successful. However, that shouldn't negatively impact Stratasys' position in the competitive landscape -- at least not yet. Though these two companies are prime competitors, there is currently more than enough business to go around. This platform will likely initially be a good match for a rather specific application: production of small-sized, customizable products.

That said, certainly investors need to monitor Stratasys' progress in offering metal printers and platforms geared toward production applications. These spaces present much long-term growth potential, and it could be costly if Stratasys let 3D Systems or any other competitor sprint too far ahead in these arenas.

3. Hewlett-Packard and other new entrants could steal market share
HP is expected to introduce a 3-D printing offering later this year. Details are sketchy, though CEO Meg Whitman has said that the product would employ "new technology" and it wouldn't be for consumers.

Numerous other companies have recently entered the 3-D printer market or plan to do so soon. Japanese industrial giant Mitsubishi introduced the LUMEX Avance-25, the world's first hybrid 3-D printer/milling machine to the North American market earlier this year. Cincinnati Inc., a privately held company, plans to commercially launch its super-speedy big area additive manufacturing, or BAAM, machine next year. Additionally, software maker Autodesk announced this spring that it's planning to introduce an open software platform for 3-D printing called Spark, as well as a 3-D printer that will serve as a reference implementation for Spark, later this year.

How likely is it that even more new entrants throw their hats into the 3-D printing ring? Very. The growth dynamics of 3-D printing are extremely compelling. According to the 2014 Wohlers Report, revenue for the industry grew by 35% to approximately $3 billion in 2013. Wohlers projects that the market will soar to $10.8 billion by 2021. Morgan Stanley is even more optimistic, as its bull scenario predicts the 3-D printing market will be worth $21 billion by 2020.

How much of a threat will these new entrants pose? Likely not much, at least for a while, in my opinion. As a co-first-mover in this space, Stratasys has a huge lead. Additionally, the company has been executing very well. Customers that have been pleased with its printers and/or services are not going to switch their allegiance to an untested competitor unless an offering is extremely compelling. That said, we can never underestimate the longer-term threat from current or potential future competitors, especially ones with deep pockets. 

Foolish final thoughts
Increased competition is the real McCoy in terms of a threat to Stratasys' stock price. Stratasys' big head start, patents (to some degree), and strong management execution, however, provide the company with a solid -- though certainly not impenetrable -- moat. Investors do need to stay abreast of the competitive landscape, and we at the Fool will be following the progress of new entrants into the market.

This article is one of a five-part series. While all articles are stand-alone, read together they offer a more thorough examination of Stratasys as an investment. The four others are: a look at the company's Q2 earnings report; don't-miss quotes from the conference call; the counter piece to this article, "3 Reasons Stratasys' Stock Could Rise"; and "Is It Time to Buy Stratasys' Stock", which focuses on valuation.